MATLAB Answers

indices when the columns are all nan

12 views (last 30 days)
Sagar
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?

  6 Comments

Show 3 older comments
Sagar
Sagar on 16 Mar 2016
But how can I apply for loop within [m d], I cannot do m(i,j) or d(i,j) right? I can set the nan values with any other values in the matrix r_all, but the problem remains the same, i.e. nanmax still returns 1 for the maximum index in d because all the values in many columns are nans.
KSSV
KSSV on 16 Mar 2016
you attach your matrix.....
Sagar
Sagar on 16 Mar 2016
attached is the data. Please follow the link: https://drive.google.com/file/d/0B67659k3uth9Nks5OTUzZ2JRYU0/view?usp=sharing

Sign in to comment.

Accepted Answer

Stephen Cobeldick
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

  3 Comments

Guillaume
Guillaume on 16 Mar 2016
+1, loops and branches are completely unnecessary
A slightly simpler implementation would be:
[m, idx] = nanmax(mat);
idx(isnan(m)) = nan;
By the way, since 2015b (iirc) max ignores nan by default.
Sagar
Sagar on 17 Mar 2016
Great, I like Guillaume's answer. :)
Sagar
Sagar on 17 Mar 2016
Thanks Stephen, apparently I didn't know there is 'all' function which I needed. :)

Sign in to comment.

More Answers (1)

KSSV
KSSV on 16 Mar 2016
clc; clear all ;
load data.mat ;
[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

  0 Comments

Sign in to comment.

Products


Translated by