Function for does matrix contain value X

Question

Is there a built in MATLAB function to find out if a matrix contains a certain value   ala PHP s in array

User · Answer

If you need to check whether the elements of one vector are in another, the best solution is ismember as mentioned in the other answers.

ismember([15 17],primes(20))

However when you are dealing with floating point numbers, or just want to have close matches (+- 1000 is also possible), the best solution I found is the fairly efficient File Exchange Submission: ismemberf

It gives a very practical example:

[tf, loc]=ismember(0.3, 0:0.1:1) % returns false 
[tf, loc]=ismemberf(0.3, 0:0.1:1) % returns true

Though the default tolerance should normally be sufficient, it gives you more flexibility

ismemberf(9.99, 0:10:100) % returns false
ismemberf(9.99, 0:10:100,'tol',0.05) % returns true

User · Answer

Many ways to do this  ismember is the first that comes to mind  since it is a set membership action you wish to take  Thus  X   primes 20   ismember  15 17  X  ans         0    1   Since 15 is not prime  but 17 is  ismember has done its job well here   Of course  find  or any  will also work  But these are not vectorized in the sense that ismember was  We can test to see if 15 is in the set represented by X  but to test both of those numbers will take a loop  or successive tests    isempty find X    15    isempty find X    17     or   any X    15  any X    17    Finally  I would point out that tests for exact values are dangerous if the numbers may be true floats  Tests against integer values as I have shown are easy  But tests against floating point numbers should usually employ a tolerance   tol   10 eps  any abs X - 3 1415926535897932384   lt   tol

User · Answer

For floating point data  you can use the new ismembertol function  which computes set membership with a specified tolerance   This is similar to the ismemberf function found in the File Exchange except that it is now built-in to MATLAB   Example    gt  gt  pi estimate   3 14159   gt  gt  abs pi estimate - pi  ans      5 3590e-08  gt  gt  tol   1e-7   gt  gt  ismembertol pi pi estimate tol  ans        1

User · Answer

you can do   A   randi 10   3 4            a random matrix any  A     5                  does A contain 5      To do the above in a vectorized way  use   any  bsxfun  eq  A      5 7 11      or as  woodchips suggests   ismember  5 7 11   A

[matlab] Function for 'does matrix contain value X?'

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