Re: For loops and column vectors

[Rik]

On 07/17/2011 11:09 AM, John W. Eaton wrote:
> On 17-Jul-2011, Rik wrote:
> 
> | 6/17/11
> | 
> | All,
> | 
> | I came across what I consider to be odd behavior, but perhaps we are trying
> | to emulate Matlab or perhaps someone knows a better reason for this.  In
> | short, the for loop construct works correctly when the range expression is
> | a row vector but not when it is a column vector.
> | 
> | Sample Code:
> | for i = [1:3]
> |   disp (i);
> |   disp ("--");
> | endfor
> | 
> | Output:
> |  1
> | --
> |  2
> | --
> |  3
> | --
> | 
> | for i = [1:3]'
> |   disp (i);
> |   disp ("--");
> | endfor
> | 
> | Output:
> |    1
> |    2
> |    3
> | --
> | 
> | In the second case the loop variable gets assigned the entire value of the
> | column vector and the loop iterates just once.
> | 
> | Any ideas?
> 
> Like Ben said, this is the way for loops work in Matlab.  It might
> make more sense if you know that in "for I = M ... end", the columns
> of M are assigned one at a time to the iteration variable I.  So then
> the behavior is consistent for row and column vectors, matrices, and
> N-d arrays.

Interesting.  In my case the actual expression was

for i = find (vector)
...
endfor

and I was getting different behavior based on the orientation of vector.  I
guess I'll just always reshape the vector before the call to find.

--Rik