Get new variable based on a condition

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Maria
Maria 2014-8-11
编辑： Andrei Bobrov 2014-8-12
I have a double variable with 3 columns and 60000 rows, sorted by c2 and then by c1. For example:
c1 c2 c3
M=[2008 1 1
2009 1 2
2010 1 34
1996 12 7
1997 12 *11*
1998 12 *5*
1999 12 *5*
2000 12 4
1998 13 14
1999 13 1 ] %in this case I don't have the value for the two previous years
For each different c2, and if c1 is equal to 1999 I am trying to have a new variable P, with the year, with c2 and with the sum of the values in c3 from that year (1999 )and the two previous years/rows (1998 and 1997).
In this example my output would be:
P=[ 1999 12 21] %(5 + 5 + 11)
Thanks
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Maria
Maria 2014-8-11
Because it is possible that it happens.

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采纳的回答

Image Analyst
Image Analyst 2014-8-11
Try this and see if it's what you want:
clc;
workspace;
M=[2008 1 1
2009 1 2
2010 1 34
1996 12 7
1997 12 11
1998 12 5
1999 12 5
2000 12 4
1998 13 14
1999 13 1 ]
uniqueC2 = unique(M(:,2))
P = [0,0,0];
counter = 1;
for k = 1 : length(uniqueC2)
% Find rows for this c2.
thisC2 = M(:,2) == uniqueC2(k);
% Find rows where c1 == 1999
validRows = M(:,1) == 1999;
% AND them
validRows = validRows & thisC2;
if any(validRows)
% This c2 has at least one year with 1999
% Find out what row it's in.
the1999Row = find(validRows);
% Sum this row only if there are at least two prior rows
% with the same value of C2.
if thisC2(the1999Row-1) && thisC2(the1999Row-2)
% Prior 2 rows also belongs to this c2.
theSum = M(the1999Row, 3) + M(the1999Row - 1, 3) + M(the1999Row - 2, 3);
P(counter, :) = [1999, uniqueC2(k), theSum];
counter = counter + 1;
end
end
end
% Print to command window:
P
It's easy to understand and fast. If you want something more compact, but probably harder to understand, someone will probably post a one-liner. But this gives exactly the output you asked for.
  1 个评论
Maria
Maria 2014-8-12
Yes it does! It gives me exactly the output I want! It is a long code, but it's fast so it's perfect. Thank you very much.

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更多回答（2 个）

Azzi Abdelmalek
Azzi Abdelmalek 2014-8-12
编辑：Azzi Abdelmalek 2014-8-12
M=[2008 1 1
2009 1 2
2010 1 34
1996 12 7
1997 12 11
1998 12 5
1999 12 5
2000 12 4
1998 13 14
1999 13 1 ]
c4=ismember(M(:,1),1997:1999);
[ii,jj,kk]=unique(M(:,2),'stable');
b=accumarray(kk,M(:,3).*c4);
out=[1999*ones(numel(jj),1) ii b];
idx=accumarray(kk,c4)==3;
out=out(idx,:)
Andrei Bobrov
Andrei Bobrov 2014-8-12
编辑：Andrei Bobrov 2014-8-12
M=[2008 1 1
2009 1 2
2010 1 34
1996 12 7
1997 12 11
1998 12 5
1999 12 5
2000 12 4
1997 13 100
1998 13 14
1999 13 1
1998 14 3
1999 14 6];
[l0,ii] = ismember(M(:,1),1997:1999);
T = accumarray([ii(l0),M(l0,2)],M(l0,3),[],[],nan);
i1 = find(all(~isnan(T))).';
s = sum(T).';
out = [1999*ones(numel(i1),1), i1, s(i1)];
or with for..end loop
u = unique(M(:,2));
out = zeros(numel(u),3);
for i1 = 1:numel(u)
M1 = M(u(i1) == M(:,2),:);
t0 = ismember(M1(:,1),1997:1999);
if nnz(t0) == 3
out(i1,:) = [1999, u(i1), sum(M1(t0,3))];
end
end
out = out(any(out,2),:);

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