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countcats

Count occurrences of categorical array elements by category

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Syntax

B = countcats(A)
B = countcats(A,dim)

Description

B = countcats(A) returns the number of elements in each category of a categorical array. The counts are in the same order as the categories listed by the categories function.

  • If A is a vector, then countcats returns the number of elements in each category.

  • If A is a matrix, then countcats treats the columns of A as vectors and returns the category counts for each column of A.

  • If A is a multidimensional array, then countcats acts along the first array dimension whose size does not equal 1.

To display a summary of a categorical array that shows both category names and the number of elements in each category, use the summary function.

example

B = countcats(A,dim) returns the category counts along dimension dim.

For example, you can return the category counts of each row in a categorical array using countcats(A,2).

example

Examples

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Open Live Script

Create a categorical array.

A = categorical(["red" "blue" "green" "blue" "red"],["red" "green" "blue"])
A = 1x5 categorical
     red      blue      green      blue      red

It has three categories, red, green, and blue.

categories(A)
ans = 3x1 cell
    {'red'  }
    {'green'}
    {'blue' }

Find the number of elements in each category of A.

  • The first element in B corresponds to the first category of A, which is red.

  • The second element in B corresponds to the second category of A, which is green.

  • The third element of B corresponds to the third category of A, which is blue.

B = countcats(A)
B = 1×3

     2     1     2

You can see the same result by using the summary function.

summary(A)
A: 1x5 categorical

     red      green      blue      <undefined> 
     2        1          2         0
Open Live Script

Create a 3-by-2 categorical array.

valueset = 1:3;
catnames = ["red" "green" "blue"];
A = categorical([1 3; 2 1; 3 1],valueset,catnames)
A = 3x2 categorical
     red        blue 
     green      red  
     blue       red

It has three categories, red, green, and blue.

categories(A)
ans = 3x1 cell
    {'red'  }
    {'green'}
    {'blue' }

Find the category counts of each column in A. The counts are in the same order as the categories listed by the categories function.

  • The value red occurs once in the first column of A and twice in the second column.

  • The value green occurs once in the first column of A, and it does not occur in the second column.

  • The value blue occurs once in the first column of A and once in the second column.

B = countcats(A)
B = 3×2

     1     2
     1     0
     1     1

You can see the same result by using the summary function.

summary(A)
A: 3x2 categorical

     red              1      2 
     green            1      0 
     blue             1      1 
     <undefined>      0      0
Open Live Script

Create a 3-by-2 categorical array.

valueset = 1:3;
catnames = ["red" "green" "blue"];
A = categorical([1 3; 2 1; 3 1],valueset,catnames)
A = 3x2 categorical
     red        blue 
     green      red  
     blue       red

It has three categories, red, green, and blue.

categories(A)
ans = 3x1 cell
    {'red'  }
    {'green'}
    {'blue' }

Find the category counts of A along the second dimension. The counts are in the same order as the categories listed by the categories function.

  • The value red occurs once in the first row of A, once in the second row, and once in the third row.

  • The value green occurs in only one element. It occurs in the second row of A.

  • The value blue occurs once in the first row of A and once in the third row.

B = countcats(A,2)
B = 3×3

     1     0     1
     1     1     0
     1     0     1

You can see the same result by using the summary function.

summary(A,2)
A: 3x2 categorical

     red      green      blue      <undefined> 
     1        0          1         0           
     1        1          0         0           
     1        0          1         0
Open Live Script

The countcats function does not return the number of undefined elements in a categorical array.

Create a 6-by-1 categorical array.

valueset = 1:3;
catnames = ["red" "green" "blue"];
A = categorical([1;3;2;1;3;1],valueset,catnames)
A = 6x1 categorical
     red 
     blue 
     green 
     red 
     blue 
     red

Remove the blue category. A has two categories, red and green. Elements of A that belonged to the blue category are now undefined.

A = removecats(A,"blue")
A = 6x1 categorical
     red 
     <undefined> 
     green 
     red 
     <undefined> 
     red

Find the number of elements in each category of A.

  • The value red occurs three times in A.

  • The value green occurs once in A.

  • countcats does not return the number of undefined elements.

B = countcats(A)
B = 2×1

     3
     1

To view the number of undefined elements as well as the number of elements in each category of A, use the summary function.

summary(A)
A: 6x1 categorical

     red              3 
     green            1 
     <undefined>      2

Input Arguments

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Input array, specified as a categorical array.

Dimension to operate along, specified as a positive integer scalar. If you do not specify the dimension, then the default is the first array dimension whose size does not equal 1.

Consider a two-dimensional categorical array, A.

If dim = 1, then countcats(A,1) returns the category counts for each column of A.

If dim = 2, then countcats(A,2) returns the category counts for each row of A.

If dim is greater than ndims(A), then countcats(A) returns an array the same size as A for each category. countcats returns 1 for elements in the corresponding category and 0 otherwise.

Tips

  • To find the number of undefined elements in a categorical array, you must use summary or isundefined.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2013b

See Also

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