NCHOOSEK - What am I doing wrong?

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Simon
Simon 2013-5-24
V = nchoosek({CRY,DXY,GOLDS,USCRWTIC,USGG2YR,USGG10YR},4);
for i= 1:15;
A{i} = V(i,:);
end;
Basically, I would need to create A1 to A15 containing the 'i' line of the matrix V. For example:
V = [1 2 3 4 ; 5 6 7 8 ; 9 0 1 2]
I would need
A1 = [1 2 3 4]
A2 = [5 6 7 8]
A3 = [9 0 1 2]
I've been searching for this for all day >.<

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Image Analyst
Image Analyst 2013-5-25
Sure, if you want to regress, just run this demo (where I made up some arbitrary values):
CRY = rand(1, 20);
DXY = rand(1, 20);
GOLDS = rand(1, 20);
USCRWTIC = rand(1, 20);
USGG2YR = rand(1, 20);
USGG10YR = rand(1, 20);
V = nchoosek({CRY,DXY,GOLDS,USCRWTIC,USGG2YR,USGG10YR},4)
for i= 1:15
A{i} = V(i,:);
end
y = sin(1:20);
% Regress y against A{1}
% Get one cell array of 4 cells from the first element of A
caRowOne = A{1}
% Extract just the first of those 4 cells.
xTraining = caRowOne{1}
% Plot training data.
plot(xTraining, y, 'bo');
hold on;
% Do a fit to a line.
coefficients = polyfit(xTraining, y, 1);
% See how well we did.
x = linspace(min(xTraining(:)), max(xTraining(:)), 40);
fittedY = polyval(coefficients, x);
plot(x, fittedY, 'r-', 'LineWidth', 2);
grid on;
title('Y vs. A{1}', 'FontSize', fontSize);
xlabel('X', 'FontSize', fontSize);
ylabel('Y', 'FontSize', fontSize);
  1 个评论
Simon
Simon 2013-5-26
Pretty cool stuff Brah! I will try to loop this for all 15 combinations and then a p-value, F and t-test for each. Thanks a lot!

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更多回答（4 个）

Azzi Abdelmalek
Azzi Abdelmalek 2013-5-24
编辑：Azzi Abdelmalek 2013-5-24
V = [1 2 3 4 5 6 7 8 9 0 1 2];
V=reshape(V,4,[]);
for i= 1:3
A{i} = V(:,i)';
end
  6 个评论
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Azzi Abdelmalek
Azzi Abdelmalek 2013-5-24
If you insist to create A1,A2 and A3 (which is not recomanded)
V = [1 2 3 4 5 6 7 8 9 0 1 2];
V=reshape(V,4,[]);
for i= 1:3
eval([ sprintf('A%d',i) '= V(:,i)'''])
end
Jan
Jan 2013-5-25
@Simon: Don't use EVAL. Creating A1, A2, ... is a bad programming pattern and therefore the most cited question from the FAQ: FAQ: How can I create A1, A2, ... in a loop .
Staying with the original matrix and using V(i, :) would be much more direct and efficient instead of inserting indirect intermediate copies to a bunch of variables, which require crude tricks to be access automatically.

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Andrei Bobrov
Andrei Bobrov 2013-5-24
A = num2cell(V,2);
Jan
Jan 2013-5-25
V(i, :) is perfect already. Are you sure that there is any reason for adding a level of abstraction by splitting the matrix to a bunch of vectors?
  2 个评论
Simon
Simon 2013-5-25
Will i be able to perform regression on each cell of A(i) with another variable? (cell 1,1 with Y , then Cell 1,2 with Y , etc)
Jan
Jan 2013-5-25
@Simon: It is very likely, that you can perform the regression even with the original matrix directly. The most Matlab commands can handle a matrix input and process the operations for the subvectors automatically. When you post the code you want to apply, more detailed suggestions are possible.
When you want to access the contents of a cell, use the curly braces: A{1} etc.

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Simon
Simon 2013-5-26
Thanks everyone! If could accept everyone's answer i would..
  3 个评论
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Randy Souza
Randy Souza 2013-5-31
There should be a triangle with "x Votes" under the profile picture for the answerer. Click that and it should change to "(x + 1) Votes"

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