Delete rows with same elements

a=[2 3 2;3 3 3;4 4 4;2 5 4; 3 5 5; 4 4 4; 7 3 4]

how do I delete only those rows where elemets repeat for entire row length. In this example matrix, the three rows with all 3s and all 4s where this happens.

Answer 1

[Star Strider]

Try this:

a=[2 3 2;3 3 3;4 4 4;2 5 4; 3 5 5; 4 4 4; 7 3 4];
a_new = a(all(diff(a,[],2) ~= 0, 2),:)

If all the columns in a particular row are the same, the vector returned by the diff function will all be uniformly 0. The all function across rows (dimension = 2) detects that, and deletes those rows.

a =
     2     3     2
     3     3     3
     4     4     4
     2     5     4
     3     5     5
     4     4     4
     7     3     4


a_new =
     2     3     2
     2     5     4
     7     3     4

[klb]

i want only the row with all elements same to be eliminated. so n ,n, x >> keep but n, n ,n>> delete

[klb]

ok i repalced 'all' with 'any' and that gives the requried answer. But thank you! Now on to researching the finess between all and any...

[Star Strider]

As always, my pleasure.

Answer 2

[Walter Roberson]

mask = all(diff(a, [], 2) == 0)

Now you can use mask as the row selector in deletion.

[Walter Roberson]

a(mask,:) = [];