How do I select every nth number of trials and put them in a separate column?
14 次查看(过去 30 天)
显示 更早的评论
I have 180x4 matrix that is sorted by two columns. There are 5 levels or variable A and 6 levels of variable B (30 groups total). Variables C and D are just responses. I would like to sample from each group with replacement. E.g. This would mean that if had a loop with 30 iterations, I would select a sample from each of the 30 groups. If I had 60 iterations, I would select 2 samples from each group.
0 个评论
采纳的回答
KSSV
2016-12-2
For a vector
X = rand(100,1) ;
X10 = X(1:10:end) ; % pick every 10'th value
X7 = X(1:7:end) ; % pick every 7'th value
For a matrix
X = rand(180,4) ;
X10 = X(1:10:end,:) ; % pick every 10'th row
X9 = X(1:9:10,:) ; % pick every 9th row
更多回答(1 个)
per isakson
2016-12-2
编辑:per isakson
2016-12-2
Try this
>> [ B, S ] = cssm1()
B =
[ 6x2 double] [3x2 double] [6x2 double] [3x2 double] [11x2 double] [9x2 double]
[ 8x2 double] [6x2 double] [9x2 double] [6x2 double] [10x2 double] [5x2 double]
[10x2 double] [2x2 double] [3x2 double] [9x2 double] [ 5x2 double] [4x2 double]
[ 8x2 double] [5x2 double] [5x2 double] [3x2 double] [ 8x2 double] [7x2 double]
[ 8x2 double] [4x2 double] [4x2 double] [5x2 double] [ 3x2 double] [5x2 double]
S =
[1x2 double] [1x2 double] [1x2 double] [1x2 double] [1x2 double] [1x2 double]
[1x2 double] [1x2 double] [1x2 double] [1x2 double] [1x2 double] [1x2 double]
[1x2 double] [1x2 double] [1x2 double] [1x2 double] [1x2 double] [1x2 double]
[1x2 double] [1x2 double] [1x2 double] [1x2 double] [1x2 double] [1x2 double]
[1x2 double] [1x2 double] [1x2 double] [1x2 double] [1x2 double] [1x2 double]
where
function [ B, S ] = cssm1()
Create the 180x4 matrix, M
len = 180;
M = nan( len, 4 );
M( :, 1 ) = randi( 5, len, 1 );
M( :, 2 ) = randi( 6, len, 1 );
M( :, 3:4 ) = randn( len, 2 );
Binning
[ N, ~, ~, binX, binY ] = histcounts2( M(:,1), M(:,2), 'BinMethod','integers' );
Populate a bin container, B
B = cell( size(N) );
for ii = 1:5
for jj = 1:6
B{ii,jj} = M( binX==ii & binY==jj, 3:4 );
end
end
Draw one random sample from each group
S = cell( size(B) );
for ii = 1:5
for jj = 1:6
ix = randi( size( B{ii,jj}, 1 ), 1 );
S{ii,jj} = B{ii,jj}( ix, : );
end
end
end
Notes:
- "question could have been phrased better"   I guess this is not a solution to your problem. This is rather an answer to the question in the Body than to that in the Title (subject line).
- "Lets say that you have: X = rand(180,4)"   with floats in column 1 and 2 'BinMethod','integers' need to be changed.
- histcounts2 was introduced in R2015b
- with a 180x4 matrix this function is fast enough(?), despite cell arrays and loops
- "selecting that entire row"   replace B{ii,jj} = M( binX==ii & binY==jj, 3:4 );   by   B{ii,jj} = M( binX==ii & binY==jj, : );
- Finally: see Tables, which support features for binning and more.
0 个评论
另请参阅
类别
在 Help Center 和 File Exchange 中查找有关 Matrix Indexing 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!