dpb
Posts:
9,716
Registered:
6/7/07


Re: Extracting particular row of a matrix based on specific condition
Posted:
Jan 2, 2014 10:03 AM


On 1/1/2014 3:50 AM, Bruno Luong wrote: > dpb <none@non.net> wrote in message <l9ulhp$sf7$1@speranza.aioe.org>... >> On 12/31/2013 2:16 AM, Bruno Luong wrote: >> > B(ismember(A,B(:,1)),2:end) >> >> That returns the rows in B for which the indices are found in A, not >> B, unfortunately, Bruno. It does get the first one correct as they're >> both in position 2, but then it returns fourth row, not first where >> the last element of A is found in first column of B... > > You are write, it learns me not to do things too fast. > >> >> >> [~,lb]=ismember(A,B(:,1)); >> >> B(lb(lb>0),2:end) >> ans = >> 0.1300 0.0010 0.8900 >> 0.1200 0.0050 0.1000 >> >> >> > > Should use the first argument of ismember() rather than recomputing it. > Also OP requires the original order, so sort() will fix the order: > > [t, iB] = ismember(A,B(:,1)); > B(sort(iB(i)),2:end)
Been puzzling over your last comment, Bruno...couldn't decide what you meant by "recomputing it". I guess you're speaking of the logical test to select nonzero elements instead of just a direct use of the logical addressing vector.
The problem I see with sort() is that I think in the general case the results could be jumbled since the two matrices are given independently. AFAICT there's no guarantee the magnitude order would be the same as the position order in the B array of an arbitrary selection of values in the A vector. Or, at least, that's my understanding of the OP's quest...


