How to efficiently replace value at the n last column?

Dear all, The objective was to replace the value at the end of a column. I have make a simple case but wonder if there is another way to make it more compact and efficient?

Thanks in advance

f_sbj=2
sA=23;
A =1:sA;
appndOut=cell(sA,1);

for f_x=1:sA
Out = nchoosek(A,  f_x);
[rows, columns] = find(Out==f_sbj);
Out(rows, :) = [];
[m,n] = size(Out );
newNan=nan(m,(sA-n));
appndOut{f_x}=[newNan Out];
end

[Walter Roberson]

That code appears to insert at the beginning of columns, not replace at the end of columns.

The code can be made more compact, but not necessarily more efficient.

[balandong]

Thanks for the quick response, Appreciate if you can some idea to make it more compact

Answer 1

[Walter Roberson]

lastNcol = @(M, N) M(:,end-N+1:end);
NanPrePad = @(M, N) lastNcol( [nan(size(M,1), N), M], N);
select_and_prepad = @(M, N) NanPrePad( M(all(M~=f_sbj, 2),:) );
appndOut = arrayfun(@(f_x) select_and_prepad(nchoosek(A, f_x), sA), (1:sA).', 'uniform', 0);

You can use shorter names for the anonymous functions if you find the above to not be compact enough.

Though I wonder why you do not do something like

   A = setdiff(1:sA, f_sbj);

That would eliminate the possibility of f_sbj being generated by the nchoosek, so it would not be necessary to delete any rows containing f_sbj.

[balandong]

Hi Walter,

Thank you for the suggested code. However I cannot run the code properly despite providing input to the function

f_sbj=2
sA=23;
M=4;
N=2;
A=3
f_x=2

Matlab produced the following error Not enough input arguments._

[Walter Roberson]

f_sbj=2
sA=23;
A =1:sA;
lastNcol = @(M, N) M(:,end-N+1:end);
NanPrePad = @(M, N) lastNcol( [nan(size(M,1), N), M], N);
select_and_prepad = @(M, N) NanPrePad( M(all(M~=f_sbj, 2),:), N );
appndOut = arrayfun(@(f_x) select_and_prepad(nchoosek(A, f_x), sA), (1:sA).', 'uniform', 0);

This takes a moment to execute.

[balandong]

Works like a charm, Thanks Walter