How can I count the number of elements of a given value in a matrix

Question

Does anyone know how to count the number of times a value appears in a matrix   For example  if I have a 1500 x 1 matrix M  vector  which stores the values of weekdays  1 - 7   how could I count how many Sundays  1   Mondays 2         Saturdays 7  are stored in M

User · Accepted Answer

Have a look at Determine and count unique values of an array     Or  to count the number of occurrences of 5  simply do  sum your matrix    5

User · Answer

Use nnz instead of sum  No need for the double call to collapse matrices to vectors and it is likely faster than sum   nnz your matrix    5    Doc

User · Answer

Here s a list of all the ways I could think of to counting unique elements   M   randi  1 7    1500 1      Option 1  tabulate  t   tabulate M   counts1   t t   2   0  2     Option 2  hist histc  counts2 1   hist  M  numel unique M      counts2 2   histc  M  unique M       Option 3  accumarray  counts3   accumarray M  ones size M         sum      or simply  accumarray M  1     Option 4  sort diff   MM idx    unique  sort M     counts4   diff  0 idx      Option 5  arrayfun  counts5   arrayfun    x sum M  x   unique M       Option 6  bsxfun  counts6   sum  bsxfun  eq  M  unique M          Option 7  sparse  counts7   full sparse M 1 1

User · Answer

this would be perfect cause we are doing operation on matrix  and the answer should be a single number  sum sum matrix  value

User · Answer

This is a very good function file available on Matlab Central File Exchange   countmember m link  This function file is totally vectorized and hence very quick  Plus  in comparison to the function being referred to in aioobe s answer  this function doesn t use the accumarray function  which is why this is even compatible with older versions of Matlab  Also  it works for cell arrays as well as numeric arrays    SOLUTION   You can use this function in conjunction with the built in matlab function   unique       occurance count   countmember unique M  M    occurance count will be a numeric array with the same size as that of unique M  and the different values of occurance count array will correspond to the count of corresponding values  same index  in unique M

User · Answer

One way you can perform this operation for all the values 1 through 7 at once is to use the function ACCUMARRAY    gt  gt  M   randi 7 1500 1       Some random sample data with the values 1 through 7  gt  gt  dayCounts   accumarray M 1      Will return a 7-by-1 vector  dayCounts       218          Number of Sundays    200          Number of Mondays    213          Number of Tuesdays    220          Number of Wednesdays    234          Number of Thursdays    219          Number of Fridays    196          Number of Saturdays

User · Answer

assume w contains week numbers   1 7    n   histc M w    if you do not know the range of numbers in M   n   histc M unique M     It is such as a SQL Group by command

[matlab] How can I count the number of elements of a given value in a matrix?

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