[R] Need a vectorized way to avoid two nested FOR loops
rama at alum.mit.edu
Wed Oct 7 21:52:21 CEST 2009
I have a data frame d. Let vars be the column indices for a subset of
the columns in d (e.g., vars <- c(1,3,4,8))
For each row r in d, I want to collect all the other rows in d that
match the values in row r for just the columns in vars.
The naive way to do this is to have a for loop stepping through each
row in d, and within the loop have another loop going through all the
rows again, checking for equality. This is quadratic in the number of
rows and takes way too long. Is there a better, "vectorized" way to do
Thanks in advance!
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