CODEWITHSUNDEEP
matlab
user6054995
user6054995

Reputation:

Number of times a particular element appears in a cell array

If I have an mxn cell array whose elements are either an integer or a vector of integers, how could I count how many times a particular integer occurs in the entire cell array? The integer could occur individually in a cell or in a vector in a cell.

My cells will look like this :

cell = { 1,2,3,4,5; [6,7,1], 2,7,8,9; 1,3,9,10, [1,2] }

Upvotes: 0

Views: 228

Answers (2)

AlessioX
AlessioX

Reputation: 3177

A simple cellfun() will help you.
Such function will perform a given function (ismember() in our case) on every cell in a given cell array.
Let's say we want to look for 1:

result=cellfun(@(x)ismember(1,x),cell);

and result will be a binary (boolean) matrix with 1 (true) in position (i,j) if cell{i,j} contains 1. To count how many items there are is enough to sum all the 1 in result:

numberOfItems=sum(result(:));

In our case then, result will have the form:

 1     0     0     0     0
 1     0     0     0     0
 1     0     0     0     1

and that is correct because 1 appears in cell{1,1}, cell{3,1} and also in the arrays that are in cell{2,1} and cell{3,5}. Now we can count the ones in result, or simply sum the entire matrix (its only values are 0s and 1s) to get numberOfItems as 4.

Note: naming a cell array cell is bad practice because cell()is a built-in Matlab function. If you name a variable or a function with built-in Matlab functions names, you won't be able to use such built-in function in your script.

Update: as @Daniel correctly pointed out, such solution might not be robust in case a vector contains the element we're looking for twice (or more). If there's a case in which, let's say, one of the arrays in cell is [1 2 1] we might want to take into account the fact that 1 appears twice in this array. So let's say we set cell{2,5}=[1 2 1], by replacing result definition as 

result=cellfun(@(x)sum(ismember(x,1)),cell)

now result has the form

 1     0     0     0     0
 1     0     0     0     2
 1     0     0     0     1

and as you can see, now in result(2,5) there is 2, not 1. Using the very same trick as before (i.e. sum all entries in result) it's possible to count the number of occurrences of a given element.

Upvotes: 0

Daniel
Daniel

Reputation: 36710

For your problem, it is irrelevant where the elements are located in your cell, start flattening the data structure to a simple vector:

v=[mycell{:}];

To count the elements, using histcounts is a good choice

[x,c]=histcounts(v,min(v):max(v));

A more generic solution which does not rely on v containing integers is:

[x,c]=histcounts(v,unique(v));

In both cases x returns how often the corresponding value in v was found.

In case your MATLAB version does not know the histcounts function, replace it with hist

Upvotes: 2

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