Count items in list<string>

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Hi all, I have a collection of strings in a generic list thus

C#

H,1000,28-09-2017
L,30,Pete
L,50,Pete
H,200,29-09-2017
L,35,Pete
L,45,Pete
L,55,Pete
etc....

How can I ( using Linq if possible ) count the number of "L" lines between each "H" line as I iterate over the list ? Basically the "H" indicates the start of a group containing n detail lines, e.g. for the first group I would like to form a string like

H,1000,28-09-2017,80,Pete,2 - where 2 = the number of L lines and 80 the sum of the amounts

What I have tried:

I currenly do it in a while loop summing and counting as I go

Posted 28-Sep-17 6:49am

pkfox

Updated 28-Sep-17 8:20am

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Richard Deeming · Accepted Answer · 2017-09-28T08:20:00

Solution 1

I strongly suspect a regular loop will be your best option. But if you really want to force it:

C#

IEnumerable<string> headerLinesWithCounts = source
    .Select((value, index) => (value: value, index: index))
    .Where(pair => pair.value[0] == 'H')
    .Select(pair => (value: pair.value, lines: source.Skip(pair.index + 1).TakeWhile(v => v[0] != 'H')))
    .Select(pair => $"{pair.value},{pair.lines.Count()}");

Output:

H,1000,28-09-2017,2 
H,200,29-09-2017,3

Or, if you need to include the lines in the output as well:

C#

IEnumerable<string> headerLinesWithCounts = source
    .Select((value, index) => (value: value, index: index))
    .Where(pair => pair.value[0] == 'H')
    .Select(pair => (value: pair.value, lines: source.Skip(pair.index + 1).TakeWhile(v => v[0] != 'H')))
    .Select(pair => (header: $"{pair.value},{pair.lines.Count()}", lines: pair.lines))
    .SelectMany(pair => Enumerable.Repeat(pair.header, 1).Concat(pair.lines));

Output:

H,1000,28-09-2017,2 
L,30,Pete 
L,50,Pete 
H,200,29-09-2017,3 
L,35,Pete 
L,45,Pete 
L,55,Pete

NB: This is using the new ValueTuple[^] type. If your compiler doesn't support it, you can use anonymous types instead.

Posted 28-Sep-17 8:20am

Richard Deeming

Updated 29-Sep-17 1:44am

v2

Comments

pkfox 28-Sep-17 14:29pm

Thanks Richard I'll give that a shot

pkfox 29-Sep-17 1:03am

Hi Richard this works a treat - how can I add the sum of the L lines ?

Richard Deeming 29-Sep-17 7:45am

What do you mean by the sum of the lines?

pkfox 29-Sep-17 12:21pm

The values in the L lines 30,35 etc...

Richard Deeming 29-Sep-17 12:53pm

Create a function to extract the value from the line:

static int ExtractLineValue(string line)
{
    int index = line.IndexOf(',', 2);
    if (index == -1) index = line.Length;
    string part = line.Substring(2, index - 2);
    int.TryParse(part, out int result);
    return result;
}

Then add the sum to the header lines:

IEnumerable<string> linesWithCountsAndSums = source
    .Select((value, index) => (value: value, index: index))
    .Where(pair => pair.value[0] == 'H')
    .Select(pair => (value: pair.value, lines: source.Skip(pair.index + 1).TakeWhile(v => v[0] != 'H')))
    .Select(pair => (header: $"{pair.value},{pair.lines.Count()},{pair.lines.Sum(ExtractLineValue)}", lines: pair.lines))
    .SelectMany(pair => Enumerable.Repeat(pair.header, 1).Concat(pair.lines));

pkfox 30-Sep-17 6:02am

Edit
Sorry Richard it does produce the sums - thank you very much for your help

Hi Richard, thanks for you time - this produced the L values but not the sum of them , what I'm trying to achieve is

H,1000,28-09-2017,2,80
L,30,Pete
L,50,Pete
H,200,29-09-2017,3,135
L,35,Pete
L,45,Pete
L,55,Pete

Richard Deeming 30-Sep-17 7:53am

That's exactly the output produced by the code from my last comment:
Demo[^]
(NB: .NET Fiddle doesn't seem to support value tuples, so I had to use anonymous types instead.)

using System;
using System.Collections.Generic;
using System.Linq;

public class Program
{
    public static void Main()
    {
        var source = new List<string>
        {
            "H,1000,28-09-2017", 
            "L,30,Pete", 
            "L,50,Pete", 
            "H,200,29-09-2017", 
            "L,35,Pete", 
            "L,45,Pete", 
            "L,55,Pete", 
        };
        
        IEnumerable<string> linesWithCountsAndSums = source
            .Select((value, index) => new { value, index })
            .Where(pair => pair.value[0] == 'H')
            .Select(pair => new { pair.value, lines = source.Skip(pair.index + 1).TakeWhile(v => v[0] != 'H') })
            .Select(pair => new { header = $"{pair.value},{pair.lines.Count()},{pair.lines.Sum(ExtractLineValue)}", lines = pair.lines })
            .SelectMany(pair => Enumerable.Repeat(pair.header, 1).Concat(pair.lines));
        
        foreach (string line in linesWithCountsAndSums)
        {
            Console.WriteLine(line);
        }
    }

    static int ExtractLineValue(string line)
    {
        int index = line.IndexOf(',', 2);
        if (index == -1) index = line.Length;
        string part = line.Substring(2, index - 2);
        int.TryParse(part, out int result);
        return result;
    }
}

Output:

H,1000,28-09-2017,2,80
L,30,Pete
L,50,Pete
H,200,29-09-2017,3,135
L,35,Pete
L,45,Pete
L,55,Pete

pkfox 30-Sep-17 9:38am

I did amend my comment Richard it's exactly what I wanted, where did you learn all this Linq stuff ? it's brilliant

jaket-cp 5-Oct-17 7:23am

agreed brilliant - 5'ed

Richard Deeming 5-Oct-17 9:30am

LINQPad[^] would probably be a good place to start. :)

pkfox 7-Oct-17 6:34am

I've got LinqPad which is great but I need to understand Linq better - I'm currently watching a series of tutorials on Youtube which is helping but it's not up to your level - where did you learn Linq ? or is it a case of RTFM :-)

Richard Deeming 9-Oct-17 14:06pm

Mostly reading the docs and playing with the sample queries in LINQPad. :)