How do I break a string into an array (or List) in C#?

Question

Using C# (VS 2010 Express) I read the contents of a text file into a string. The string is rather long but reliably broken up by "\t" for tabs and "\r\n" for carriage returns/newlines.

The tabs indicate a new column of data, and new line indicates a new row of data.

I want to create an array or List of dimensions (X)(Y) such that each spot in the array can hold 1 row of data from the text file, and all of the Y columns contained in that 1 row ("\t" means a new column of data, and "\r\n" means a new row of data").

To make things simple let's say my text has 10 rows of data, and 2 columns. I'd like to create an array or List or whatever you think is best to store the data. How do I do this? Thanks.

This is the code that I used to read the data in the text file into a string:

// Read the file as one string.
            System.IO.StreamReader myFile = new System.IO.StreamReader("f:\\data.txt");
            string myString = myFile.ReadToEnd();

File.ReadAllLines will give you array of rows. You can then split each line with \t for columns. Datatable would be best to store this data — Esen
– Esen, Commented Aug 29, 2012 at 19:34
Is the file large or small? Usually you want to stream the data line by line so that you don't need to hold the whole thing in memory. — Servy
– Servy, Commented Aug 29, 2012 at 19:36
Potentially, large. Like an 8MB text file. Is it too late to reword my question? I really want to ask a broader question now given everyone's comments. That is, how do I read a TAB-delimited text file into a List? Or, should I just start a new thread for that? — MrPatterns
– MrPatterns, Commented Aug 29, 2012 at 20:03
In one text file I have 50,000 rows of data. Each row contains 2 columns of strings. I used the code above to read the text file into a string. — MrPatterns
– MrPatterns, Commented Aug 29, 2012 at 20:06
@phan, that would lean toward not using ReadToEnd() then, but using an approach like that in my answer, where you only read one line at a time. Ideally then foreach on the result, but even if you ToArray() it to get an array at least you don't load an 8MB string at any point. — Jon Hanna
– Jon Hanna, Commented Aug 29, 2012 at 20:52

Jon Hanna · Accepted Answer · 2012-08-29 21:15:07Z

1

Just as is (you already have a string with everything):

str.Split(new string[]{"\r\n"}, StringSplitOptions.None)
  .Select(s => s.Split('\t'));

Gives you an IEnumerable<string[]> producing variantes like list of list, array of array and so on just needs the suitable ToArray() or ToList() etc.

However, if you can deal with each line one at a time, you can be better off with something that lets you do so:

public IEnumerable<string[]> ReadTSV(TextReader tr)
{
  using(tr)
    for(string line = tr.ReadLine(); line != null; line = tr.ReadLine())
      yield return line.Split('\t');
}

Then you only use as much memory as each line needs. We could go further and change the reading to emit each individual cell one at a time, but this is normally enough to read files of several hundred MB in size, with reasonable efficiency.

Edit based on comments on question:

If you really wanted to, you could get a List<string[]> from:

var myFile = new StreamReader("f:\\data.txt");
var list = ReadTSV(myFile).ToList();

Alternatively, change the line yield return line.Split('\t'); to yield return line.Split('\t'); and you get a List<List<string>>.

However, if possible then work on the results directly, rather than putting it into a list first:

var myFile = new StreamReader("f:\\data.txt");
var chunks = ReadTSV(myFile);
foreach(var chunk in chunks)
{
   DoSometingOnAChunk(chunk[0], chunk[1]);
}

It'll use less memory, and get started faster rather than pausing to read the whole thing first. Code like this can merrily work its way through gigabytes without complaint.

edited Aug 29, 2012 at 21:15

answered Aug 29, 2012 at 19:39

Jon Hanna

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2 Comments

MrPatterns Over a year ago

Got an error with this line: var list = ReadTSV(TextReader tr).ToList();....) expected.

Jon Hanna Over a year ago

Sorry, that was rather a silly error. Fixed now. (And do avoid the ToList() if you can just foreach directly).

Vladmir · Accepted Answer · 2012-08-29 19:34:40Z

1

String.Split

http://msdn.microsoft.com/en-us/library/system.string.split.aspx

answered Aug 29, 2012 at 19:34

Vladmir

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Comments

Douglas · Accepted Answer · 2012-08-29 19:36:12Z

1

File.ReadLines(sourceFilePath)
    .Select(line => line.Split('\t'))
    .ToArray();

answered Aug 29, 2012 at 19:36

Douglas

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M. Mennan Kara · Accepted Answer · 2012-08-29 19:36:16Z

1

This will read the file and create a list of string arrays for you

List<string[]> rows= File.ReadLines("PathToFile")
    .Select(line=>line.Split('\t')).ToList();

If you want string[][] version, simply use ToArray(); instead of ToList(); at the end.

answered Aug 29, 2012 at 19:36

M. Mennan Kara

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Servy · Accepted Answer · 2012-08-29 19:39:01Z

1

The TextFieldParser is a fantastic class for dealing with text based delimited files. You can provide it a file, a delimiter (in this case "\t") and it will provide a method to get the next line of values (as a string array).

It has advantages over a simple Split in the general case as it can handle comments, quoted fields, escaped delimiters, etc. You may or may not have such cases, but having all of those awkward edge cases handled pretty much for free is rather nice.

answered Aug 29, 2012 at 19:39

Servy

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Jon Hanna · Accepted Answer · 2012-08-29 19:52:12Z

1

var result = contents.Split("\r\n".ToArray(), StringSplitOptions.RemoveEmptyEntries).Select(s => {
    s.Split('\t').ToList();
}).ToList();

result will be a List<List<String>>.

edited Aug 29, 2012 at 19:52

Jon Hanna

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answered Aug 29, 2012 at 19:34

PinnyM

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2 Comments

Jon Hanna Over a year ago

There isn't a Split() overload that takes just a string.

PinnyM Over a year ago

Fair enough, but you can easily turn it into a char[]. Updated.

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