Count the number of same elements in an array
显示 更早的评论
Hi given a vector
V = [ 1 2 4 3 4 2 3 5 6 4 5 6 8 4 2 3 5 7 8 5 3 1 3 5 7 8 9 5 3 2 4 6 7 8]
I would like to count how many times the value 1,2,3,4,5,6,7,8,9 are repeated inside V, and obtain a vector that report this values:
C = [2 4 6 5 6 3 3 4 1]
where 1 is repeated 2 times, 2 is repetead 4 times, 3 is repeated 6 times and so on..
采纳的回答
madhan ravi
2019-9-10
编辑：madhan ravi
2019-9-10
[~,~,ix] = unique(V);
C = accumarray(ix,1).'
5 个评论
luca
2019-9-10
luca
2019-9-10
madhan ravi
2019-9-10
编辑：madhan ravi
2019-9-10
C=accumarray(V(:),1).'
%or
C=sum(V(:)==(1:max(V)))
As per your latter comment Stephen’s approach below will do what you want.
accumarray(V(:),1)
Simple idea which works well:
>> V = [2 2 3 4 5 6 7 7 8 8 9 9]
>> accumarray(V(:),1)
ans =
0
2
1
1
1
1
2
2
2
madhan ravi
2019-9-10
Thank you Stephen :) !
更多回答（3 个）
Your 1st example:
>> V = [ 1 2 4 3 4 2 3 5 6 4 5 6 8 4 2 3 5 7 8 5 3 1 3 5 7 8 9 5 3 2 4 6 7 8];
>> C = hist(V,1:max(V))
C =
2 4 6 5 6 3 3 4 1
Your 2nd example:
>> V = [2 2 3 4 5 6 7 7 8 8 9 9]
>> C = hist(V,1:max(V))
C =
0 2 1 1 1 1 2 2 2
I found this function extremely useful, and doing exactly what you need:
V = [ 1 2 4 3 4 2 3 5 6 4 5 6 8 4 2 3 5 7 8 5 3 1 3 5 7 8 9 5 3 2 4 6 7 8];
[gc,grps] = groupcounts(V'); % <- need column vector here
grps'
gc'
Where grps lists the unique values in order, and gc provides the count of each unique values found in v.
This is very similar to madhan ravi's accumarray, but even simpler.
P.S. I turned gc and grps into row vectors only for compactness of the post, it's purely aesthetical. However groupcounts requires a column vector, not a row.
Hugo Diaz
2020-11-28
0 个投票
I use sparse(V(:),V(:), 1) for large arrays with missing indices.
类别
在 帮助中心 和 File Exchange 中查找有关 Image Arithmetic 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
