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Function changes its behavior at each iteration of a for loop

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kerin on 23 Mar 2015
Commented: kerin on 24 Mar 2015
Hi everyone, the problem is as follows, i want in a for loop change the behavior of a function at each iteration. Suppose the following for loop F or k = 1:4 B = Min_or_max([k 2 4]); end Let’s assume I have 2 functions called Compute_min and Compute_max computing respectively the maximum and the minimum value of a given vector/array taken as input parameter. I want that at the first iteration of the for loop compute_min is used instead of min_or_max and at the second iteration of the loop the function compute_max is used and so on.. Note that the for loop is placed in a function which takes as input a parameter, which should specify which function of (compute_min and compute_max ) should be used at which step. Example : for a = compute_min and b = compute_max the input parameter of the function in which the for loop is located can take the form [a b a a ] ; which means compute_min is used at the first iteration , compute_max is used at the second iteration , then compute_min at the third and again compute_min at the fourth iteration.
Many Thanks guys

Accepted Answer

Stephen on 23 Mar 2015
Edited: Stephen on 23 Mar 2015
If you have two (or more) pre-defined functions that you wish to select between in a loop, then you could consider using function handles to select and pass the functions. Something like this:
fun = {@min,@max};
idx = [1,2,1,1];
mat = [1,2,3,4;5,6,7,8;9,10,11,12];
out = nan(size(idx));
for k = 1:numel(idx)
out(k) = fun{idx(k)}(mat(:,k));
>> mat
mat = 1 2 3 4
5 6 7 8
9 10 11 12
>> out
out = 1 10 3 4
shows that it has taken the minimum of columns 1, 3, and 4, and the maximum of column 2, exactly as the vector idx selected. How it works:
  • fun is a cell array of the function handles that you want to call.
  • idx is a vector of the indices of the functions in fun to call on each loop.
  • mat is some fake numeric data, with as many columns as idx has elements.
  • out is the min/max value of each column of mat, depending on which function was selected for that column by the corresponding index in idx.
kerin on 24 Mar 2015
ohh yessssssssss !!!!!! u're amazing !!! Thanks.. be blessed !!

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More Answers (1)

wil on 23 Mar 2015
We'll call your input parameter list 'param', you can do something like the following:
for k= 1:4
switch param(k)
case 'a'
B = Compute_min([k 2 4]);
case 'b'
B = Compute_max([k 2 4]);
% handle invalid param
Which checks the index of the parameters and calls the corresponding function depending on the value.


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