How can I make a variable of unknown size?

Question

1.67/5 (3 votes)

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I want to make a variable of type double as:

C#

double[,] tempData = new double[5000,2];

but I don't want to define the size as 5000.
I want the size (i.e. 5000) to be defined by the number of lines which are read from external sources (e.g a *.csv file). I don't want to use the Lists!
Can anybody help?

regards
AM

Posted 15-Jul-15 4:37am

ARMS_DEIR

Updated 15-Jul-15 4:38am

v2

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PIEBALDconsult 15-Jul-15 10:45am

"I don't want to use the Lists!"
Why not? They seem better suited to the requirement.

Wendelius 15-Jul-15 10:47am

Agree, what's the point of not using ready made functionality?

PIEBALDconsult 15-Jul-15 10:49am

I actually suspect it's a matter of homework and the teacher wants them to try it both ways to see the power of Lists.

ARMS_DEIR 15-Jul-15 10:55am

Assuming that you are suspecting that it is a homework, isn't it worth to come here and see different ideas. Unfortunately you are wrong andd it is not a homework. I am a mechanical engineer that just started to programming. That is all. and it made me frustrated when I asked a question somebody comes and directly say it is .... may be better to google it or so on, If I have the answer I wouldnt be here!

Better to ask a question and appear stupid now, than not ask a question and remain stupid forever.
If you give a man a fish, you feed him for a day. If you teach him how to fish, you feed him for a lifetime.

Sergey Alexandrovich Kryukov 15-Jul-15 11:17am

Please understand: all your "I want" should be reasonably motivated. Perhaps you want to know why? This is simple: people want to help you, and not to waste time on someone who won't use the advice anyway.

And please set aside your "frustration" and other emotions, if you want to be taken as an engineer and not as a child. It you think that something or someone makes you look stupid, think again: maybe it's just your fantasy. If your are afraid of looking stupid, this is only your problem. No one blames you for asking wrong questions, but be ready to some comments which may not praise you. What's wrong with that?

When people advise to Google, they are trying to teach you how to fish, and when they ask you immediately, it might be just giving a fish.

Now, back to business. Why do you want to avoid List<>? It seems to be the most reasonable approach, unless you need more advanced type of collection.

—SA

F-ES Sitecore 15-Jul-15 11:25am

If I asked the best way to allow an object to be moved but that I didn't want to use wheels or tracks what would you say? Probably that while it can be done, the effort to do and lack of efficiency of the final solution would mean that the better solution is to overcome the obstacle that prevents you from not wanting to use wheels or tracks. Use the best tool for the job rather than trying to invent elaborate workarounds, and if that means refactoring a lot of your code then that's what you'll need to do.

ARMS_DEIR 15-Jul-15 10:50am

If I want to use Lists then I have to change too many variables that are alredy made, If you think it is not that hard I would follow your Method!

PIEBALDconsult 15-Jul-15 10:54am

You want to use Lists, or maybe other structures, but hardly ever arrays.

Sergey Alexandrovich Kryukov 15-Jul-15 11:23am

No. What variables?

Look, you have one problem. Are you afraid that something people usually use is hard for you? Then your destiny is to get something "easy" and not reach your goals. No, it's not hard.

Only please understand that no one wants to convince you. It's up to you how you solve your problems. You are given some quite reasonable advice, so it's the best at least try to follow it.

—SA

Philippe Mori 15-Jul-15 12:38pm

Lazyness is generally not a good excuse to avoid updating existing code. In develpment, it is very common to have to update existing code. If you always try to minimize changes then in the long term the application will become unmaintainable.

If doing such a change is too hard, then probably your application is poorly designed and the level of abstraction is not high enough. That is too much code use the variable directly instead of using an intermediate abstraction.

Richard MacCutchan 15-Jul-15 10:55am

You would need to read the .csv file into some other variables first so you could count them and then allocate the array. So using a List would be simpler.

Sergey Alexandrovich Kryukov 15-Jul-15 11:31am

By the way, there is no such thing as "variable of unknown size". You are looking something with variable size, and this is some object, not "variable". The key here is that those are reference types, not value types. There are two objects: the reference itself and the referenced object, and the object is always on heap, and the reference is anywhere. The object can grow...
—SA

ARMS_DEIR 16-Jul-15 4:59am

I just have tried to read the file first and put it in a tempdata, and then count the read lines, then I put the rows of tempdata which are indiced by count and modify my main variables. seems basic but works!!

Sergey Alexandrovich Kryukov 16-Jul-15 9:54am

Really basic is using List...
—SA

3 solutions

Solution 2

In Array.Resize<t> Method[^] documentation there's a proposal for resizing two-dimensional arrays. Perhaps that would help you.

Depending on the situation I'd still consider going to lists (or similar) especially if you think you need more complex handling in the future, like removing items from the middle, query operations and so on...

Posted 15-Jul-15 4:57am

Wendelius

Comments

Sergey Alexandrovich Kryukov 15-Jul-15 12:07pm

This method is as inefficient as creation of a new array each time. The really rare case when a reference type is passed by reference indicates that the referential identity of the source array is lost at the call, so a brand new array is created. Practical applicability of this method is extremely limited and certainly unsuitable to the case in question.

The inquirer simply has no valid objections against System.Collections.Generic.List<>. This is the only reasonable approach, unless more advanced collection type is needed. As you see from the comments to the question, the objection is simply based on false idea that using the list appears to be to difficult, by some mysterious reason. This is just the misconception which also maybe demonstrating wrong approach to engineering in general. The only effective help could be pointing out this misconception.

—SA

Wendelius 15-Jul-15 12:55pm

Yes, the method in documentation is quite.. peculiar and is basically based on creating always a new array. That's why be both agree on using list :)

Solution 3

int numLines;
//...set numLines...
double[,] tempData = new double[numLines,2];

Posted 15-Jul-15 4:58am

pringlesbox

Updated 15-Jul-15 4:59am

v2

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OriginalGriff · Accepted Answer · 2015-07-15T04:56:00

Solution 1

Well, read the CSV file, identify how many lines there are, and allocate that number of array elements. Then process the CSV data into your array.

If you don't want to use a "flexible" array like List<T> (and it is at heart an array that is copied when it expands) then you either need to construct a linked list of some description, or know in advance how many items to allocate.

Posted 15-Jul-15 4:56am

OriginalGriff

Comments

ARMS_DEIR 16-Jul-15 5:01am

just have tried to read the file first and put it in a tempdata, and then count the read lines, then I put the rows of tempdata which are indiced by count and modify my main variables. seems basic but works!!

OriginalGriff 16-Jul-15 5:18am

Glad to hear it!
I'd go with a List myself! :laugh: