# indices when the columns are all nan

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Sagar on 16 Mar 2016
Commented: Sagar on 17 Mar 2016
I am using [m, d] = nanmax (r_all); to get the maximum values and corresponding indices in matlab. There are several columns in r_all in which all the elements are nans. Unfortunately, nanmax returns '1' in indices for those columns that have all nans. However, there are actual indices that are value '1' so it creates confusion. How can I force matlab to return 'a' or 'b' as the output instead of returning 0' or '1'? Could you please suggest other solutions to this problem?
Sagar on 16 Mar 2016

Stephen Cobeldick on 16 Mar 2016
Edited: Stephen Cobeldick on 16 Mar 2016
There is no need to waste time using slow and ugly loops and if statements. You can locate those "incorrect" indices very simply using basic MATLAB indexing:
>> mat = [0,1,2,NaN,3,NaN;4,NaN,5,NaN,6,NaN;7,8,NaN,NaN,NaN,9]
mat =
0 1 2 NaN 3 NaN
4 NaN 5 NaN 6 NaN
7 8 NaN NaN NaN 9
>> [m,idx] = nanmax(mat) % max value and its indices
m =
7 8 5 NaN 6 9
idx =
3 3 2 1 2 3
>> idx(all(isnan(mat),1)) = NaN % replace all-NaN indices with NaN
idx =
3 3 2 NaN 2 3
Sagar on 17 Mar 2016
Thanks Stephen, apparently I didn't know there is 'all' function which I needed. :)

KSSV on 16 Mar 2016
clc; clear all ;
[m,n] = size(data) ;
idx = zeros(n,1) ;
val = idx ;
% column wise
for c = 1:n
[i,j] = nanmax(data(:,c)) ;
if isnan(i)
j = 50 ;
end
idx(c) = j ;
val(c) = i ;
end

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