How can I count the occurrences of each element in a vector in MATLAB?

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I would like to be able to return the count of occurences of each element in a vector.
For example if I have a vector:
x=[10 25 4 10 9 4 4]
I expect the result to be
y=[2 1 3 2 1 3 3].

采纳的回答

MathWorks Support Team
编辑:MathWorks Support Team 2020-2-27
As of MATLAB R2019a, you can use the “groupcounts” function to compute the number of times an element appears in a vector as a summary. In other words, the elements of the below output “GC” are the counts of the corresponding element values in “GR” (from the original input vector “x”):
x = [10 25 4 10 9 4 4]';
[GC,GR] = groupcounts(x)
GC =
3
1
2
1
GR =
4
9
10
25
For more information on "groupcounts", please see the documentation link below:
---
As of MATLAB R2018b, you can use the “grouptransform” function if you want to compute the number of times an element appears in a vector and output that count for each corresponding element of the input vector. For example:
x = [10 25 4 10 9 4 4]';
y = grouptransform(x,x,@numel)
y =
2
1
3
2
1
3
3
For more information on "grouptransform", please see the documentation link below:
---
Prior to MATLAB R2018b, while there is no single function to count occurrences of each element, there are a few ways to count elements in a vector:
1. Logical Indexing:
The following code snippet will give the desired output:
y = zeros(size(x));
for i = 1:length(x)
y(i) = sum(x==x(i));
end
For MATLAB R2016b and later, you can use implicit expansion to further simplify the code:
y = sum(x==x')
2. Binning:
You can use the "hist" and "unique" functions as shown here to do the same:
x = [10 25 4 10 9 4 4]
[a,b]=hist(x,unique(x))
3. Third-Party Tools:
For another workaround, see the following file, 'CountMember.m', that was contributed by a MATLAB user to do the same from a single function:
Note that MathWorks does not guarantee or warrant the use or content of submissions to the MATLAB Central File Exchange. Any questions, issues, or complaints should be directed to the contributing author.
  10 个评论
Walter Roberson
Walter Roberson 2022-4-26
https://www.mathworks.com/help/matlab/ref/double.groupcounts.html#mw_92fbcf5a-2ab5-45d0-ac09-68c1986c269f
when you use groupcounts then the groups are in the order returned by unique('sorted')

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更多回答(8 个)

Andrei Bobrov
Andrei Bobrov 2014-8-14
[a,b] = histc(x,unique(x));
y = a(b);
  5 个评论

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Razvan Carbunescu
There is a simpler way of answering this now using groupcounts(R2019a) or grouptransform(R2018b):
>> x=[10 25 4 10 9 4 4]';
>> grouptransform(x,x,@numel)
ans =
2
1
3
2
1
3
3
>>[GC,GR]=groupcounts(x)
GC =
3
1
2
1
GR =
4
9
10
25
  7 个评论
Razvan Carbunescu
This seems like a very different type of problem so unlikely the functions in this topic will help you directly. I'd post this question as a separate thread with the example input/output

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Julian Hapke
Julian Hapke 2017-6-1
编辑:Julian Hapke 2017-6-1
here is another one:
sum(bsxfun(@eq,x,x'),1)
or if you want the output to be the same orientation as input
sum(bsxfun(@eq,x,x'),(size(x,2)==1)+1)

Josh
Josh 2014-8-14
This is kind of awkward since it requires using the input array within the anonymous function, but:
y = arrayfun(@(t)nnz(x==t), x);
should do the trick, too.

mittal54
mittal54 2015-5-16
编辑:Walter Roberson 2017-8-16
numbers=unique(v); %list of elements
count=hist(v,numbers); %provides a count of each element's occurrence
this will give counts. and if you want to have a nice graphical representation then try this
bar(accumarray(v', 1))
  1 个评论
Walter Roberson
Walter Roberson 2015-5-16
When using hist() pay attention to Dan's comment above pointing out a flaw in the approach. This flaw is not shared by Andrei's histc approach above.

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Truong Phan
Truong Phan 2017-8-16
I need help to count the occurrences of each element in a matrix. Thanks
  1 个评论
Walter Roberson
Walter Roberson 2017-8-16
[uvals, ~, uidx] = unique(YourArray);
output = [uvals, accumarray(uidx, 1)];
This would produce an N x 2 array with the first column being the unique array values and the second column being the associated count.

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lamghari
lamghari 2015-11-30
Hi, I want to count the number of followed occurrences of each element in a vector.
So if my input is
x = [1 1 1 2 2 1 1 2 5 5]
I need an output
y = [1 2 1 2 5;3 2 2 1 2] How do I do this?

Ramon Villamangca
Ramon Villamangca 2018-10-25
编辑:Ramon Villamangca 2018-10-25
This is how I did it:
numOccur = sum(arrayfun(@(x) x == elem,vec))
where 'elem', is the element to search in the given vector 'vec'.

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