The for loop doesn't iterate

Question

In MATLAB the following `for` loop: ``` for i = [1:100]' %'// Do something, such as disp(i) end ``` isn't apparently really implemented by iteration, rather `i` becomes the matrix [1 2 3 ... 100] and the "loop" is only executed once on this matrix `i`. You can verify this by printing the value of `i` or other tracking information. Only a single pass is made through the loop. Is it possible to force MATLAB to do genuine looping? The reason I ask is that the above approach is fine for many cases but much more painful when you have nested loops that need to run. Example: The following code won't do what you would expect if you thought you were getting actual iteration over a loop: ``` for i = outlier data(i) = median(data(i-100:i+100)) end ``` One would expect at each outlier index this would replace data(i) with the median of the data from i-100 to i+100, but it doesn't. In fact, the median returns a single value computed on a conglomerate of all the ranges you cared about, and every da…

Accepted Answer

If you write

```
for i = (1:100)' %'# square brackets would work as well
   doSomething
end
```

the loop is executed only once, since a `for`-loop iterates over all columns of whatever is to the right of the equal sign (it would iterate 200 times with a 100-by-200 array to the right of the equal sign).

However, in your example, you have `i=[1:100]`, which evaluates to a row vector. Thus, the loop should execute 100x.

If you iterate over an array that might be `nx1` instead of `1xn`, you can, for safety reasons, write:

```
for i = myArray(:)'  %'# guarantee nx1, then transpose to 1xn
end
```

The for loop doesn't iterate

Solution

Problem