On 2010-10-07 10:10, Jim Silverton wrote:
Hello,
I gave a list of 2 x 2 matrices called matlist. I have about 5000 2 x 2
matrices. I would like to count how many of each 2 x 2 unique matrix I have.
So I am thinking that I need a list of the unique 2 x 2 matrices and their
counts. Can anyone help.
Here's one way, using the plyr package:
require(plyr)
## make a list of 2X2 matrices
L <- vector('list', 5000)
set.seed(4321)
for(i in 1:5000) L[[i]] <- matrix(round(runif(4), 1), 2, 2)
## convert each matrix to a string of 4 numbers, then
## form dataframe
dL <- ldply(L, function(.x) toString(unlist(.x)))
## add an index vector
dL$ind <- seq_len(5000)
## count unique strings; return string, frequency, indeces
result <- ddply(dL, .(V1), summarize,
freq=length(V1),
idx=toString(ind))
-Peter Ehlers
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