I want to add new columns to a data.table that is the weighted average of the
columns and a weight variable. This is a general problem I run into when using
.SDcols but also needing another variable from the data.table to be available
within the function within lapply. Without including that variable within
.SDcols (in this case the weight variable), I don't have access to it in the
lapply function argument. Is it a bad idea to subset .SD how I've done it?
library(data.table)
library(Hmisc)
dt <- data.table(a=runif(10), b= runif(10), weight=runif(10))
varnames <- c("a","b")
dt[ , ( paste( "mean", varnames, sep = "_" ) ) := lapply( .SD[ , .SD, .SDcols =
-"weight" ], wtd.mean, weight ), .SDcols = c("weight",varnames) ]
Thanks
-Marc
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