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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].

채택된 답변

MathWorks Support Team
MathWorks Support Team 2020년 2월 27일
편집: MathWorks Support Team 2020년 2월 27일
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.
  댓글 수: 8
Walter Roberson
Walter Roberson 2020년 5월 19일
S = 'aaabb'
nnz(triu((S'=='a') & S=='b'))

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추가 답변(8개)

Andrei Bobrov
Andrei Bobrov 2014년 8월 14일
[a,b] = histc(x,unique(x));
y = a(b);
  댓글 수: 5
Tech Support
Tech Support 2018년 5월 2일
Hi,
If you are still experiencing this issue, please contact MathWorks support:
-Justin

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Razvan Carbunescu
Razvan Carbunescu 2019년 5월 9일
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
  댓글 수: 7
Razvan Carbunescu
Razvan Carbunescu 2019년 6월 7일
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 2017년 6월 1일
편집: Julian Hapke 2017년 6월 1일
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)
  댓글 수: 1
Johannes Korsawe
Johannes Korsawe 2017년 6월 1일
the second solution exhibits pathological tendencies...

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Josh
Josh 2014년 8월 14일
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.

Truong Phan
Truong Phan 2017년 8월 16일
I need help to count the occurrences of each element in a matrix. Thanks
  댓글 수: 1
Walter Roberson
Walter Roberson 2017년 8월 16일
[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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mittal54
mittal54 2015년 5월 16일
편집: Walter Roberson 2017년 8월 16일
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))
  댓글 수: 1
Walter Roberson
Walter Roberson 2015년 5월 16일
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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lamghari
lamghari 2015년 11월 30일
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 2018년 10월 25일
편집: Ramon Villamangca 2018년 10월 25일
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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