Crosstabs with data.table in R [duplicate]
We can use dcast from data.table (See the Efficient reshaping using data.tables vignette on the project wiki or on the CRAN project page).
dcast(dt, opinion~party, value.var='ID', length)Benchmarks
If we use a slightly bigger dataset and compare the speed using dcast from reshape2 and data.table
set.seed(24)df <- data.frame(ID=1:1e6, opinion=sample(letters, 1e6, replace=TRUE), party= sample(1:9, 1e6, replace=TRUE))system.time(dcast(df, opinion ~ party, value.var='ID', length))# user system elapsed # 0.278 0.013 0.293 system.time(dcast(setDT(df), opinion ~ party, value.var='ID', length))# user system elapsed # 0.022 0.000 0.023 system.time(setDT(df)[, .N, by = .(opinion, party)])# user system elapsed # 0.018 0.001 0.018 The third option is slightly better but it is in 'long' format. If the OP wants to have a 'wide' format, the data.table dcast can be used.
NOTE: I am using the the devel version i.e. v1.9.7, but the CRAN should be fast enough.