CDataFile - An easy class for reading numeric data in CSV or Text-Delimited format.

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Nov 26, 2002

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This class reads numeric data and stores it for easy access. The data can be accessed by (row, column) from any data reduction routines you may have.

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Introduction

This article presents the CDataFile class. CDataFile is a class that is designed to provide an interface to using and manipulating CSV (comma separated values) or other text-delimited, tabular, data files. CDataFile was first published in November, 2002 and has undergone several improvements and enhancements, and ended up getting totally redesigned. This implementation has removed all dependence on MFC and now makes great use of the Standard Template Library (STL). Throughout the class, you will find several interesting tricks and some creative use of predicates, function objects, and the STL algorithms. But most importantly, you will find a powerful interface that is designed for usability by the novice and experienced programmer alike.

Why CDataFile?

When I set out to search for a class to read CSV and other text data, I had these criteria:

The class had to be very fast in parsing, lookups, and data manipulation.
The class had to provide a simple (column, row) type interface.
The class had to be able to efficiently handle data files in excess of 100MB or more.

To my surprise, I was hard pressed to find anything that met my criteria. I found some stuff that used OBDC and even DOM, but nothing lightweight, simple to use, or very fast. So I decided to write my own, and CDataFile is the result.

Using CDataFile

In order to use CDataFile, you need to add DataFile.cpp and DataFile.h to your project and include the following header file:

#include "DataFile.h"

I have listed the member functions and operators of CDataFile in the tables below. Note that the term variable in this class is synonymous with field or column, and the term sample is synonymous with record or row.

CDataFile Member Functions

Function	Description
`AppendData`	Appends data to a specified variable.
`ClearData`	Clears all data from the `CDataFile`.
`CreateVariable`	Creates a new variable in the `CDataFile`.
`DeleteVariable`	Deletes a variable from a `CDataFile`.
`FromVector`	A static function to create a `CDataFile` from a vector.
`GetData`	Gets data from the `CDataFile`.
`GetLastError`	Gets the last error encountered by the `CDataFile`.
`GetNumberOfSamples`	Gets the number of samples contained in a variable.
`GetNumberOfVariables`	Gets the number of variables in the `CDataFile`.
`GetReadFlags`	Gets the current read flags.
`GetVariableIndex`	Gets the lookup index of a specified variable.
`GetVariableName`	Gets the name of the variable at a specified location.
`ReadFile`	Reads the contents of a file and stores it in the `CDataFile`.
`SetData`	Sets data in the `CDataFile`.
`SetDelimiter`	Sets the delimiter to use for parsing files.
`SetReadFlags`	Sets the read flags of the `CDataFile`.
`SetReserve`	Sets the capacity of contiguous memory for the `CDataFile` before a reallocation is needed.
`WriteFile`	Writes the contents of the `CDataFile` to a file.

CDataFile Operators

Operator	Description
`operator()`	Gets data from the `CDataFile` depending on which override is called.
`operator[][]`	Gets a reference to the data at the specified location. (Note: valid for `DOUBLE` mode only, not `STRING`)
`operator+`	Combines the contents of `CDataFile`(s).
`operator+=`	Appends the contents of another `CDataFile` to the `CDataFile`.
`operator=`	Sets the contents of the `CDataFile` to the contents of another `CDataFile`.
`operator<<`	Puts the contents of a `CDataFile` to a stream.
`operator>>`	Extracts the contents of a `CDataFile` from a stream.

Constructing a CDataFile

CDataFile(void);
CDataFile(const int& dwReadFlags);
CDataFile(const char* szFilename, 
  const int& dwReadFlags = DF::RF_READ_AS_DOUBLE);
CDataFile(const DF::DF_SELECTION& df_selection);
CDataFile(const CDataFile& df);

Parameters

dwReadFlags
Determines how the data is read and stored in the CDataFile. Can be any combination of the following:
- RF_READ_AS_DOUBLE (Takes priority if RF_READ_AS_STRING is also set)
- RF_READ_AS_STRING
- RF_APPEND_DATA (Takes priority if RF_REPLACE_DATA is also set)
- RF_REPLACE_DATA
szFilename
The fully qualified path to the data file to read upon construction.
df_selection
A subset of another CDataFile to which the constructor will set initial values.
df
Another CDataFile to which the constructor will set initial values.

Remarks

None of the CDataFile constructors will throw an exception, but will catch any exceptions internally. Optionally, the user can call CDataFile::GetLastError() to retrieve any error information due to a CDataFile construction exception.

Example

// Construct an empty CDataFile:
   CDataFile df;
 

// Construct a CDataFile to read a CSV file containing data of type double:
   CDataFile df("C:\\MyData.csv");
 
// Construct a CDataFile to read a CSV file containing data of type string:
   CDataFile df("C:\\MyStringData.csv", DF::RF_READ_AS_STRING);

 
// Construct an empty CDataFile that will read string data and append 
// data with each subsequent file read:
   CDataFile df(DF::RF_READ_AS_STRING | DF::RF_APPEND_DATA);


 
// Construct a CDataFile from a subset of another CDataFile:
   CDataFile df1("C:\\MyData.csv");
   CDataFile df2(df1(iLeftColumn, iTopRow, iRightColumn, iBottomRow));

CDataFile::AppendData()

The AppendData() member function appends data to the end of a specified variable. You can append values one at a time, or append the contents of an entire vector. AppendData() will return true if it was successful, or false if an error was encountered.

bool AppendData(const int& iVariable, const char* szValue);
bool AppendData(const int& iVariable, const double& value);
bool AppendData(const int& iVariable, const std::vector<double>& vData);
bool AppendData(const int& iVariable, const std::vector<std::string>& vszData);

Parameters

iVariable
The index of the variable to which the data will be appended.
szValue
The value to append. (Assumes DF::RF_READ_AS_STRING.)
value
The value to append. (Assumes DF::RF_READ_AS_DOUBLE.)
vData
A const reference to a vector containing the values to append. (Assumes DF::RF_READ_AS_DOUBLE.)
vszData
A const reference to a vector containing the values to append. (Assumes DF::RF_READ_AS_STRING.)

Return Value

Returns true if the function was successful, false if an error was encountered.

Remarks

If the user appends string data, it is appended to the CDataFile internal string vector, whereas if the user appends values of type double, the data is allocated to the class' internal double vector.

Example

// To append 0.2123 to the variable at index 0:
   if(!df.AppendData(0, 0.2123))
      cout << df.GetLastError();
    
// To append the contents of a std::vector<double>, v, to the variable at index 4:
   if(!df.AppendData(4,v);
      cout << df.GetLastError();

CDataFile::ClearData()

The ClearData() member function is responsible for clearing all the data from a CDataFile, reclaiming any allocated memory, and zeroing the class' internal buffer size.

void ClearData(void);

Remarks

The class will reclaim a block of contiguous memory equal to the size specified by CDataFile::SetReserve() when reading a new data file, otherwise the internal buffer capacity will be zero. The class will allocate internal buffer storage as needed, but may exhibit the behavior studied in this article [^] if the class is required to read excessively large files. Calling CDataFile::SetReserve() with an adequate capacity before CDataFile::ReadFile() will eliminate this behavior.

CDataFile::ClearData() is called automatically when a CDataFile is destroyed.

Example

// Flush the contents of a CDataFile, df.
df.ClearData();

CDataFile::CreateVariable()

The member function, CreateVariable(), is provided as a means to append a new variable to the end of your CDataFile. Think of it as adding a new column to the right of your data in Excel. You can create variables of pre-determined sizes and an initial value, or you can create a variable from an existing vector.

bool CreateVariable(const char* szName, const double& initial_value, 
    const int& iSize = 0);
bool CreateVariable(const char* szName, const std::string& initial_value, 
    const int& iSize = 0);
bool CreateVariable(const char* szName, const std::vector<double>& vData);
bool CreateVariable(const char* szName, 
    const std::vector<std::string>& vszData);

Parameters

szName
The name you want to assign to the variable. Think of it as a column label in Excel or a field name in a database.
initial_value
The value you want all of the new data to contain. Think of it as assigning all the rows in a column this initial value.
iSize
The number of samples (rows or records) you want your variable to contain.
vData
A vector of type double containing the data to assign to the new variable.
vszData
A vector of type string containing the data to assign to the new variable.

Return Value

Returns true if the function was successful, false if an error was encountered.

Remarks

The default size of a new variable is 0. The user must then call CDataFile::AppendData() to add values to the variable. If the user attempts to call CDataFile::SetData() on a variable of size 0, an error will occur.

Example

// Create a variable in df named "MyVar"
// with 27 samples initialized to 0.0.
   if(!df.CreateVariable("MyVar", 0.0, 27))
      cout << df.GetLastError();
 
// Create a variable in df named "My Vector Var"
// containing the data in vector, v.
   if(!df.CreateVariable("My Vector Var",v);
      cout << df.GetLastError();

CDataFile::DeleteVariable()

The DeleteVariable() member function is provided to delete a variable from a CDataFile. Think of it as deleting a column in Excel, or an entire field in a database.

bool DeleteVariable(const int& iVariable);

Parameters

iVariable
The index of the variable to be deleted from the CDataFile.

Return Value

Returns true if the function was successful, false if an error was encountered.

Remarks

Use CDataFile::GetLastError() to retrieve any error information.

Example

// Delete the variable at index 3 from CDataFile, df.
   if(!df.DeleteVariable(3))
       cout << df.GetLastError();

CDataFile::FromVector()

The static member function, FromVector(), is provided as a means to create a CDataFile object from an existing data vector. This function particularly is useful when using CDataFile::operator+ and CDataFile::operator+=.

static CDataFile FromVector(const char* szVariableName, 
  const std::vector<double>& vData);
static CDataFile FromVector(const char* szVariableName, 
  const std::vector<std::string>& vData);

Parameters

szVariableName
The name you want to assign to the variable. Think of it as a column label in Excel or a field name in a database.
vData
A vector of type double or string containing the data to assign to the new variable.

Return Value

Returns a CDataFile containing the resultant variable.

Remarks

Use this static function when you need to convert a vector of data to a CDataFile.

Example

// Add the contents of vector, v, to CDataFile, df, using operator +=
   df += CDataFile::FromVector("MyVectorData", v);
 
// Combine the contents of vector, v1,
// and vector, v2, and set the CDataFile, df, 
// equal to the result.
   df = CDataFile::FromVector("My V1 Data", v1) + 
            CDataFile::FromVector("My V2 Data", v2);

CDataFile::GetData()

There are several overrides provided for the member function, GetData(). This is to allow for great flexibility in how the user wants to retrieve the data. You can get data by variable index or by variable name, as well as obtain a single sample or all samples.

double GetData(const int&  iVariable,      const int& iSample);
double GetData(const char* szVariableName, const int& iSample);
int    GetData(const int&  iVariable,      std::vector<double>& rVector);
int    GetData(const char* szVariableName, std::vector<double>& rVector);
int    GetData(const int&  iVariable,      const int& iSample, char* lpStr);
int    GetData(const char* szVariableName, const int& iSample, char* lpStr);
int    GetData(const int&  iVariable, const int& iSample, std::string& rStr);
int    GetData(const char* szVariableName, 
         const int& iSample, std::string& rStr);
int    GetData(const int&  iVariable, std::vector<std::string>& rVector);
int    GetData(const char* szVariableName, 
         std::vector<std::string>& rVector);

Parameters

iVariable
The index of the variable from which to retrieve the data.
iSample
The sample number (record or row, 0-indexed) to retrieve.
rVector
A reference to a vector containing the proper data type to receive the data.
lpStr
A pointer to a string buffer to receive the data.
rStr
A reference to a std::string that will receive the data.

Return Value

double GetData(const int&  iVariable, const int& iSample);
double GetData(const char* szVariableName, const int& iSample);

Returns a value of type double equal to the data at the specified location if successful, DF::ERRORVALUE if an error is encountered.

int GetData(const int&  iVariable,      std::vector<double>& rVector);
int GetData(const char* szVariableName, std::vector<double>& rVector);
int GetData(const int&  iVariable,  std::vector<std::string>& rVector);
int GetData(const char* szVariableName, 
   std::vector<std::string>& rVector);

Returns the new size of rVector if successful, -1 if an error is encountered.

int GetData(const int&  iVariable, 
         const int& iSample, char* lpStr);
int GetData(const char* szVariableName, 
         const int& iSample, char* lpStr);
int GetData(const int&  iVariable, 
         const int& iSample, std::string& rStr);
int GetData(const char* szVariableName, 
         const int& iSample, std::string& rStr);

Returns the new length of the lpStr or rStr if successful, -1 if an error is encountered.

Remarks

If calling GetData() with parameters of type double, DF::RF_READ_AS_DOUBLE is assumed. When calling with parameters of type char* or std::string, DF::RF_READ_AS_STRING is assumed.

Example

// Initialize a variable, d, to sample 7 of "MyVar" from CDataFile, df.
   double d = df.GetData("MyVar", 7);
   if(d == DF::ERRORVALUE)
      cout << df.GetLastError();
 
// Get string data from sample 3 of variable 9 from CDataFile, df.
   CString szValue = "";
   int iLength = 0;
 
   iLength = df.GetData(9, 3, szValue.GetBuffer(0));
   
   szValue.ReleaseBuffer();
 
   if(iLength == -1)
      cout << df.GetLastError();
   else
   {
      //... do something
   }
 
// Get all the data from "My Variable 2" out of CDataFile,
// df, and put it in vector, vData.
   std::vector<double> vData;
   int iSize = df.GetData("My Variable 2", vData);
 
   if(iSize == -1)
      cout << df.GetLastError();
   else
   {
      //... do something
   }

CDataFile::GetLastError()

The member function, GetLastError(), is provided as a means to extract information from a CDataFile, regarding the last error encountered by the class.

const char* GetLastError(void) const;

Return Value

Returns a const char* containing information about the last error encountered by the class.

Example

// Display the last error encountered by CDataFile, df.            
   cout << df.GetLastError();

CDataFile::GetNumberOfSamples()

The GetNumberOfSamples() member function is provided as a means to determine how many samples are contained in any given variable.

int GetNumberOfSamples(const int& iVariable) const;

Parameters

iVariable
The index of the variable for which to obtain the number of samples.

Return Value

Returns the number of samples if the function was successful, -1 if an error was encountered.

Remarks

Use CDataFile::GetLastError() to retrieve any error information.

Example

// Get the number of samples contained
// in the variable at index 3 from CDataFile, df.
   int nSamps = df.GetNumberOfSamples(3); 
 

   if(nSamps==-1)
       cout << df.GetLastError();

CDataFile::GetNumberOfVariables()

The GetNumberOfVariables() member function is provided so that the user can obtain the number of variables currently contained in the CDataFile.

int GetNumberOfVariables(void) const;

Return Value

Returns the number of variables contained in the CDataFile.

Example

// Get the number of variables contained in CDataFile, df.
   int nVars = df.GetNumberOfVariables();

CDataFile::GetReadFlags()

The GetReadFlags() member function is provided as a means to obtain the current read flags that have been either set or cleared.

int GetReadFlags(void) const;

Return Value

Returns the current read flags.

Remarks

The function returns an int that contains the flags encoded within it. Use the bitwise & operator to determine which flags are actually set.

Example

// Check to see if the user has set DF::RF_APPEND_DATA
   cout << "Append mode is "
        << (df.GetReadFlags() & DF::RF_APPEND_DATA ? "" : "NOT " ) 
        << "set!";

CDataFile::GetVariableIndex()

The GetVariableIndex() member function is provided as a means to lookup the index of a variable, given its name and/or other information.

int GetVariableIndex(const char* szVariableName, 
                     const int& iStartingIndex = 0);
int GetVariableIndex(const char* szVariableName, 
  const char* szSourceFilename, const int& iStartingIndex = 0);

Parameters

szVariableName
The name of the variable for which to find the index.
iStartingIndex
The index from which to begin the search.
szSourceFilename
The name of the file from which the variable originated.

Return Value

Returns the index (0-based) of the variable if the function was successful, -1 if an error was encountered.

Remarks

GetVariableIndex() will return the first instance of the variable name. If you have variables in your data with the same name, and you need an instance of the variable name other than the one first encountered, you will want to offset your search with iStartingIndex.

You may have data in a CDataFile that comes from different source files (i.e. using DF::RF_APPEND_DATA). In these cases, you may desire an instance of a variable from a particular source file. In this case, you would use the override provided with szSourceFilename.

Example

// Get the index of "MyVar" from CDataFile, df.
   int iVar = df.GetVariableIndex("MyVar");
                  
   if(iVar == -1)
       cout << df.GetLastError();
 
// Get the index of "My Var 2" occurring after
// variable 3 whose source file is "C:\data.csv".
   int iVar = df.GetVariableIndex("My Var 2", "C:\\data.csv", 3);

 
   if(iVar == -1)
       cout << df.GetLastError();

CDataFile::GetVariableName()

The GetVariableName() member function is provided to lookup the name of a variable (or field) given its index (or 0-based column number).

int GetVariableName(const int& iVariable, char* lpStr);
int GetVariableName(const int& iVariable, std::string& rStr);

Parameters

iVariable
The index of the variable for which to obtain the name.
lpStr
A pointer to a string buffer to receive the name.
rStr
A string to receive the name.

Return Value

Returns the length of the variable name if the function was successful, -1 if an error was encountered.

Remarks

Use CDataFile::GetLastError() to retrieve any error information.

Example

// Get the variable name at index 3.
   CString szVarName = "";
   int iLength = df.GetVariableName(3, szVarName.GetBuffer(0)); 
   szVarName.ReleaseBuffer();
 
   // or...

   std::string szVar = "";
   iLength = df.GetVariableName(3, szVar);
 
   if(iLength==-1)
      cout << df.GetLastError();
   else
      cout << szVar.c_str();

CDataFile::ReadFile()

The ReadFile() member function is provided as a way to easily read a data file by wrapping up all the file IO stuff.

bool ReadFile(const char* szFilename);
bool ReadFile(const char* szFilename, const unsigned& dwReadFlags);

Parameters

szFileName
The fully qualified path to the file.
dwReadFlags
The flags to specify how to read the file. (See Constructing a CDataFile for more info.)

Return Value

Returns true if the function was successful, false if an error was encountered.

Remarks

Use CDataFile::GetLastError() to retrieve any error information.

Example

// Read the contents of "C:\test.csv" into CDataFile, df.
   if(!df.ReadFile("C:\\test.csv"))
      cout << df.GetLastError(); 
 
// Append the data from "C:\test2.csv" to CDadaFile, df.
   if(!df.ReadFile("C:\\test2.csv", DF::RF_APPEND_DATA))
      cout << df.GetLastError();

CDataFile::SetData()

The SetData() member function is provided as a way to set data values stored in a CDataFile.

bool SetData(const int& iVariable, const int& iSample, const double& value);
bool SetData(const int& iVariable, const int& iSample, const char* szValue);

Parameters

iVariable
The variable for which to set the data.
iSample
The sample for which to set the data.
value
The value that the data will be set to. (Assumes DF::RF_READ_AS_DOUBLE)
szValue
The value that the data will be set to. (Assumes DF::RF_READ_AS_STRING)

Return Value

Returns true if the function was successful, false if an error was encountered.

Remarks

Use CDataFile::GetLastError() to retrieve any error information.

Example

// Set variable 3, sample 0 to 2.121 in CDataFile, df.
   if(!df.SetData(3,0,2.121))
      cout << df.GetLastError();

CDataFile::SetDelimiter()

The SetDelimiter() member function is provided to set the delimiter that will separate values in a CDataFile.

void SetDelimiter(const char* delim);

Parameters

delim
The character to use for parsing data.

Example

// Set the delimiter in CDataFile, df, to 'tab'.
   df.SetDelimiter("\t");

CDataFile::SetReserve()

The SetReserve() member function is provided to set the capacity of a CDataFile.

void SetReserve(const int& nReserve);

Parameters

nReserve
The number of elements to reserve space for.

Example

// Set the reserve of CDataFile, df, to 1000000.
   df.SetReserve(1000000);

CDataFile::WriteFile()

The WriteFile() member function is provided to simplify writing a CDataFile to disk.

bool WriteFile(const char* szFilename, const char* szDelim = ",");

Parameters

szFilename
The fully qualified path for the destination file.
szDelim
The delimiter to use to separate data values.

Return Value

Returns true if the function was successful, false if an error was encountered.

Remarks

Use CDataFile::GetLastError() to retrieve any error information.

Example

// Write the contents of CDataFile, df, to "C:\test.csv".
   if(!df.WriteFile("C:\\test.csv"))
      cout << df.GetLastError();

CDataFile::operator()

The () operator is provided to easily extract data from a CDataFile.

double operator()(const int& iVariable, const int& iSample);
int operator()(const int& iVariable, const int& iSample, char* lpStr);
DF::DF_SELECTION operator()(const int& left, const int& top,
    const int& right, const int& bottom);

Parameters

iVariable
The variable for which to obtain the data.
iSample
The sample for which to obtain the data.
lpStr
A string buffer to receive the data.
left, top, right, bottom
The coordinates from which to obtain the resulting selection. Think of it as highlighting a range of cells in Excel.

Return Value

double operator()(const int& iVariable, const int& iSample);

Returns the value at the specified location successful, DF::ERRORVALUE if an error was encountered.

int operator()(const int& iVariable, const int& iSample, char* lpStr);

Returns the new length of the lpStr if successful, -1 if an error is encountered.

DF::DF_SELECTION operator()(...);

Returns a selection (DF_SELECTION) containing the values in the specified range.

Remarks

Use CDataFile::GetLastError() to retrieve any error information.

Example

// Set d equal to the data at (2,4) from CDataFile, df.
   d = df(2,4);
 
// Get the string data contained at (1,7).
   CString szData = "";
   int iLength = df(1,7,szData.GetBuffer(0));
   szData.ReleaseBuffer();

 
// Create a new CDataFile from the range (0,0,9,120).
    dfNew(df(0,0,9,120));

CDataFile::operator[][]

The [][] operator is provided to easily extract data of type double from a CDataFile.

Return Value

Returns a reference to the data at the specified location.

Remarks

This operator is only valid for DF::RF_READ_AS_DOUBLE. Since an actual reference is returned, you are able to assign values as well as read them.

Example

// Set d equal to the data at variable 2, sample 4 from CDataFile, df.
   double d = df[2][4];
 
// Set the data at variable 9, sample 0, from CDataFile, df, equal to d.
   df[9][0] = d;

CDataFile::operator+

The + operator is provided to combine the contents of multiple CDataFile objects.

CDataFile operator+ (const CDataFile&) const;

Example

// Set CDataFile, df, to the combined data of df2, df3, and df4.
   df = df2 + df3 + df4;

CDataFile::operator+=

The += operator is provided to append a CDataFile to another CDataFile.

CDataFile& operator+=(const CDataFile&);

Example

// Append the contents of CDataFile, df2, to CDataFile, df.
   df += df2;

CDataFile::operator=

The = operator sets the internals of one CDataFile equal to another CDataFile.

CDataFile& operator =(const CDataFile&);
CDataFile& operator =(const DF::DF_SELECTION&);

Example

// Set CDataFile, df2, equal to CDataFile, df.
   df2 = df1;
 
// Set df3 equal to the selection df(0,0,4,120).
   df3 = df(0,0,4,120);

CDataFile::operator<<

The << operator puts the contents of a CDataFile to a stream.

std::ostream& operator << (std::ostream&, const CDataFile&);
std::ostream& operator << (std::ostream&, const DF::DF_SELECTION&);

Example

// Put CDataFile, df, to outStream.
   outStream << df; 
 
// Put the selection (0,0,5,15) to outStream.
   outStream << df(0,0,5,15);

CDataFile::operator>>

The >> operator gets the contents of a CDataFile from a stream.

std::istream& operator >> (std::istream&, CDataFile&);

Example

// Get CDataFile, df, from inStream.
   inStream >> df;