CODEWITHSUNDEEP
matlabsubtraction
Tom
Tom

Reputation: 121

Matlab: subtract every value in a row from every other, for every row

I have data like this: [...

0...0...0...0
6...0...0...0
8...5...2...0
9...8...3...1
0...0...0...0

Within each row I would like to subtract every value individually from every other in that row. So that I get a new matrix which shows all the differences like this: [...

null
0
3...6...3
1...6...8...5...7...2
null

I hope you see what I mean. I don't want to subtract 0 from anything (O is null for me-if you have a way to replace 0 with null thats fine). Or at least, if this has to be done, I want those results to be discarded. But I DO want there to be some placeholder when a row is entirely made of 0s.

The ordering of the resulting subtractions doesn't matter, except that the row order overall should be maintained.

Upvotes: 1

Views: 2042

Answers (1)

Jonas
Jonas

Reputation: 74940

You can use PDIST to calculate the distances:

data =[0 0 0 0
6 0 0 0
8 5 2 0
9 8 3 1
0 0 0 0];
nRows = size(data,1);

%# for speed, preassign 'out'
out = cell(nRows,1);

for r = 1:nRows
   pts = data(r,data(r,:)>0); %# this assumes valid entries are >0
   switch length(pts),
   case 0,
      out{r} = []; %# empty for 'null'
   case 1, 
      out{r}=0; %# zero if only one valid number
   otherwise
      out{r}=pdist(pts'); %'# calculate all differences
   end
end

%# You access elements of a cell array with curly brackets
>> out{3}
ans =
     3     6     3

Upvotes: 2

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