Multi-Dimensional Array - Array of arrays?

Question

I have a string containing numbers as a 2D matrix. I'm trying to use Split function to split the contents of a string into an array. So, when I do:

String[] subStrs = new String[20];
subStrs = str.Split('\n');

The code above works fine. However, when I try to create a 2D array and try to populate sub-arrays using the same way:

String[,] numbers = new String[20,20];
for (int i = 0; i < subStrs.Length; i++ )
{
    numbers[i] = subStrs[i].Split(' '); //Error
}

I get the following compiler error:

Wrong number of indices inside []; expected 2.

If 2D array is really an array of arrays, then why is the statement numbers[i] = subStrs[i].Split(' '); illegal?

PS : I do know that I can use a nested loop instead to populate numbers. I'm just curious why can't I use the above method?

There's no point in creating arrays that you're going to immediately overwrite with a new array. Only create a new array when you actually intend to access the values of that array. — Servy
– Servy, Commented Mar 30, 2015 at 19:03
string[,] and string[][] are two different things. Split returns a string[] so it can be added to an array of arrays (i.e. string[][]), but not a 2D array string[,] without some more work (i.e. you'd need an inner loop to assign values to the correct cells in a string[,]) — Matt Burland
– Matt Burland, Commented Mar 30, 2015 at 19:03
@Servy I'm sorry, I didn't understand your comment. Could you please elaborate that? — Dumbledore
– Dumbledore, Commented Mar 30, 2015 at 19:05
@Dumbledore You're creating an array and then immediately throwing it away and assigning a new array to that variable. That's pointless. Just don't create a new array if you're just going to throw it away and assign a new array to that variable without using it. — Servy
– Servy, Commented Mar 30, 2015 at 19:06

Servy · Accepted Answer · 2015-03-30 19:01:25Z

8

If 2D array is really an array of arrays

It's not. A 2D array is just that, a 2D array.

An array of arrays is an array of arrays:

string[][]

If you have an array of arrays, then the item at each index of the outer array is another array. If you have a 2D array then both dimensions are needed to get at a value, which is itself the value of the array, not another dimension.

answered Mar 30, 2015 at 19:01

Servy

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