For loop with vertical vs horizontal array
显示 更早的评论
Is the below difference intended functionality or a bug?
x = [1, 2, 3, 4];
for y = x
disp( 'Printing' );
disp( y );
end
Result:
Printing
1
Printing
2
Printing
3
Printing
4
Whereas if I transpose x, the loop only runs once with y = [1; 2; 3; 4].
x = [1, 2, 3, 4]';
for y = x
disp( 'Printing' );
disp( y );
end
Result:
Printing
1
2
3
4
Perhaps I'm being thick, but I can't find this behavior documented anywhere and I would have expected it to loop through the elements in the matrix/array as if it were one dimensional (linear indexing).
采纳的回答
Image Analyst
2012-12-11
I agree it's confusing at first. However it is documented in the "for" section:
for index = valArray
creates a column vector index from subsequent columns of array valArray on each iteration. For example, on the first iteration, index = valArray(:,1). The loop executes for a maximum of n times, where n is the number of columns of valArray, given by numel(valArray, 1, :). The input valArray can be of any MATLAB data type, including a string, cell array, or struct.
In your sexcond case, n is 1 - one column so the loop executes only once. In your first case, n was 4 - four columns so the loop executed 4 times.
5 个评论
Chris
2012-12-11
Walter Roberson
2012-12-11
If you are using indices then use
for index = 1 : numel(valArray)
If you are using array values and do not know the orientation then
for index = valArray(:).'
Chris
2012-12-11
Walter Roberson
2012-12-11
The simple ' is conjugate transpose, in which the signs of the complex part of values are reversed. The .' operator is plain transpose.
Chris
2012-12-11
更多回答（1 个）
Walter Roberson
2012-12-11
It is deliberate behavior.
valarray : creates a column vector index from subsequent columns of array valArray on each iteration. For example, on the first iteration, index = valArray(:,1). The loop executes for a maximum of n times, where n is the number of columns of valArray, given by numel(valArray, 1, :). The input valArray can be of any MATLAB data type, including a string, cell array, or struct.
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