[R] Check values in colums matrix

[Muhammad Subianto]

Dear all,
I apologize if my question is quite simple.
I have a dataset (20 columns & 1000 rows) which
some of columns have the same value and the others
have different values.
Here are some piece of my dataset:
obj <- cbind(c(1,1,1,4,0,0,1,4,-1),
             c(0,1,1,4,1,0,1,4,-1),
             c(1,1,1,4,2,0,1,4,-1),
             c(1,1,1,4,3,0,1,4,-1),
             c(1,1,1,4,6,0,1,5,-1),
             c(1,1,1,4,6,0,1,6,-1),
             c(1,1,1,4,6,0,1,7,-1),
             c(1,1,1,4,6,0,1,8,-1))
obj.tr <- t(obj)
obj.tr
> obj.tr
     [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
[1,]    1    1    1    4    0    0    1    4   -1
[2,]    0    1    1    4    1    0    1    4   -1
[3,]    1    1    1    4    2    0    1    4   -1
[4,]    1    1    1    4    3    0    1    4   -1
[5,]    1    1    1    4    6    0    1    5   -1
[6,]    1    1    1    4    6    0    1    6   -1
[7,]    1    1    1    4    6    0    1    7   -1
[8,]    1    1    1    4    6    0    1    8   -1
>

How can I do to check columns 2,3,4,6,7 and 9 have
the same value, and columns 1,5 and 8 have different values.

Best, Muhammad Subianto