Yoav -
Here's one possibility:
wh = outer(rownames(mtrx),colnames(mtrx),
+ function(x,y)substr(x,nchar(x)-2,nchar(x)) ==
substr(y,nchar(y)-2,nchar(y)))
mtrx[wh]
[1] 1 6 8
If you knew that all of the row and column names were 4 characters long, it
would simplify to
mtrx[outer(rownames(mtrx),colnames(mtrx),function(x,y)substr(x,2,4) ==
substr(y,2,4))]
Hope this helps.
- Phil Spector
Statistical Computing Facility
Department of Statistics
UC Berkeley
spec...@stat.berkeley.edu
On Wed, 20 Apr 2011, yoav baranan wrote:
Hi,
I have a (correlation) matrix and I want to select a subset of its cells
depending on the combination of their column and row names.
This illustrates my problem: mtrx <- matrix(c(1,2,3,4,5,6,7,8,9), nrow=3, ncol=3,
dimnames = list(c('c132','c432', 'c233'), c('r132','r233', 'r432')))> mtrx
r132 r233 r432c132 1 4 7c432 2 5 8c233 3 6 9
At this point I want to compute the mean of the cells in which the column and
the row names share the same suffix (i.e., the cells mtrx[1,1], mtrx[2,3],
mtrx[3,2]). By suffix I mean the last three digits of the row/col name.
I need a generic code (and not vec<-c(mtrx[1,1], mtrx[2,3], mtrx[3,2])) because
I don't know in advance how many rows and columns I will have (currently 118).
Thanks, Yoav
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