Counting occurrences of each column in a matrix

Question

Daniel Ring 2018-10-8

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/422859-counting-occurrences-of-each-column-in-a-matrix

评论： Daniel Ring 2018-10-8

I have a matrix with 16 columns and a very large number of rows. Each column has two possible outcomes in it (for example 1 or 0 in one column, .6 and .4 in another). I would like to count each of these occurrences in the columns. Preferably, I'd like to have a vector that counts each outcome of its respective column. Thank you!

[EDITED, Jan, moved from section for answers]

Example: A = [1 .6 .7 .8; 0 .4 .3 .2; 1 .6 .7 .8; 1 .6 .3 .8]

ans = [3 3 2 2 ; 1 1 2 2]

3 个评论
显示 1更早的评论隐藏 1更早的评论

Jan 2018-10-8

The example is not clear: 0.8 occurs 3 times, so shouldn't the last value of the output be 3 or perhaps 1? Why is the first column of the output [3;1] and not [1;3]?

Daniel Ring 2018-10-8

I'm sorry, it should be ans = [3 3 2 3 ; 1 1 2 1] The first column in [3;1] because 1 occurs 3 times and 0 occurs 1 time.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

ANKUR KUMAR 2018-10-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/422859-counting-occurrences-of-each-column-in-a-matrix#answer_340357

Since you have not given any sample data, I am taking some random data.

A=randi(50,50,50);
A(A<=25)=0.4;
A(A>25)=0.6;

A contains only 0.4 and 0.6 only, spreaded out completely. The below program gives you the occurrence of 0.4 and 0.6 in every coloumn.

nums1=arrayfun(@(x) length(find(A(:,x)==0.4)),1:size(A,2));
nums2=arrayfun(@(x) length(find(A(:,x)==0.6)),1:size(A,2));
occur=[nums1' nums2'];

nums2 can also be calculated as

nums2=size(A,1)-nums1;

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 2

Jan 2018-10-8

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/422859-counting-occurrences-of-each-column-in-a-matrix#answer_340359

编辑：Jan 2018-10-8

Maybe:

A = [1 .6 .7 .8; ...
     0 .4 .3 .2; ...
     1 .6 .7 .8; ...
     1 .6 .3 .8];
Count  = sum(A == A(1, :), 1);   % Auto-expand: >= R2016b
Result = [Count; size(A, 1) - Count];

For older Matlab versions:

Count = sum(bsxfun(@eq, A, A(1, :)), 1);

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 3

dpb 2018-10-8

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/422859-counting-occurrences-of-each-column-in-a-matrix#answer_340358

Several ways to do this; probably easiest is via converting to categorical with the unique values in each column transformed to a single pair of categories--[0|1], [Y|N], [HI|LO], ..., whatever makes sense for the meanings.

Then histogram on those variables to return counts.

Or, use unique and the returned (optional) second index array to bin over.