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indices when the columns are all nan

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Sagar
Sagar 2016 年 3 月 16 日
コメント済み: Sagar 2016 年 3 月 17 日
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?

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Sagar
Sagar 2016 年 3 月 16 日
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 2016 年 3 月 16 日
you attach your matrix.....
Sagar
Sagar 2016 年 3 月 16 日
attached is the data. Please follow the link: https://drive.google.com/file/d/0B67659k3uth9Nks5OTUzZ2JRYU0/view?usp=sharing

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Stephen Cobeldick
Stephen Cobeldick 2016 年 3 月 16 日
編集済み: Stephen Cobeldick 2016 年 3 月 16 日
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

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Guillaume
Guillaume 2016 年 3 月 16 日
+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 2016 年 3 月 17 日
Great, I like Guillaume's answer. :)
Sagar
Sagar 2016 年 3 月 17 日
Thanks Stephen, apparently I didn't know there is 'all' function which I needed. :)

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KSSV
KSSV 2016 年 3 月 16 日
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

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