[R] applying a function over a matrix 2N x M to produce a matrix N x M
Christine SINOQUET
christine.sinoquet at univ-nantes.fr
Fri Apr 22 18:13:04 CEST 2011
Hello,
mat1 only consists of 0s and 1s:
0 0 1 0 0 0
1 1 0 1 1 0
1 1 1 0 1 0
0 1 1 0 0 1
1 0 0 1 0 0
0 1 0 1 0 1
N = 3
M = 6
I would like to "compress" mat1 every two rows, applying summation over
the two rows (per column), at each step, to yield:
mat2
1 1 1 1 1 0
1 2 2 0 1 1
1 1 0 2 0 1
Then, in mat2, I shall have to count the number of 0s, 1s and 2s, per
column, which is my final aim.
I am aware of possibilities such as
counts <- sapply(mat2,2,fun1)
but I do not know how to write fun1.
Besides, it was perhaps not necessary to waste memory producing the
temporary matrix mat2.
Can somebody help ?
I thank you in advance for your answer.
Best regards,
Christine Sinoquet
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