C# rows of multi-dimensional arrays
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08-12-2019 - |
Question
In the C# programming language, how do I pass a row of a multi-dimensional array? For example, suppose I have the following:
int[,] foo;
foo = new int[6,4];
int[] least;
least = new int[6];
for(int i = 0; i < 6; i++)
{
least[i] = FindLeast(ref foo[i]); //How do I pass the ith row of foo???
}
Also, could anyone explain to me the benefit of having rectangular and jagged arrays in C#? Does this occur in other popular programming languages? (Java?) Thanks for all the help!
La solution
You can't pass a row of a rectangular array, you have to use a jagged array (an array of arrays):
int[][] foo = new int[6][];
for(int i = 0; i < 6; i++)
foo[i] = new int[4];
int[] least = new int[6];
for(int i = 0; i < 6; i++)
least[i] = FindLeast(foo[i]);
EDIT
If you find it so annoying to use a jagged array and desperately need a rectangular one, a simple trick will save you:
int FindLeast(int[,] rectangularArray, int row)
Autres conseils
You don't, with a rectangular array like that. It's a single object.
Instead, you'd need to use a jagged array, like this:
// Note: new int[6][4] will not compile
int[][] foo = new int[6][];
for (int i = 0; i < foo.Length; i++) {
foo[i] = new int[4];
}
Then you can pass each "sub"-array:
int[] least = new int[foo.Length];
for(int i = 0; i < 6; i++)
{
least[i] = FindLeast(foo[i]);
}
Note that there's no need to pass foo[i]
by reference1, and also it's a good idea to assign local variables values at the point of declaration, when you can. (It makes your code more compact and simpler to understand.)
1 If you're not sure about this, you might want to read my article on parameter passing in C#.
Update: As Jon Skeet rightly points out, this does not provide a reference to the row, but rather creates a new copy. If your code needs to change a row, this method doesn't work. I have renamed the method to make this clear.
Update 2: If you want to be able to edit the fields, and have the changes happen to the parent array, too, you can use the wrapper I provide in this library I maed. The resulting row foo.Row(i)
is not an array, but instead implements IList
, so if you need to pass an array this is not a solution, either.
This extension method will allow you to query a multi-dimensional array for rows. It should be noted that this is computationally heavy (not efficient) and if it is possible you should use a jagged array for these situations. If, however, you find yourself in a situation where you cannot use a jagged array, this might be useful.
public static T[] CopyRow<T>(this T[,] arr, int row)
{
if (row > arr.GetLength(0))
throw new ArgumentOutOfRangeException("No such row in array.", "row");
var result = new T[arr.GetLength(1)];
for (int i = 0; i < result.Length; i++)
{
result[i] = arr[row, i];
}
return result;
}
Your code can now be rewritten:
int[,] foo;
foo = new int[6,4];
int[] least;
least = new int[6];
for(int i = 0; i < 6; i++)
{
least[i] = FindLeast(ref foo.CopyRow(i));
}