Randomly split data by criterion into training and testing data set using R

Question

Gidday,

I\'m looking for a way to randomly split a data frame (e.g. 90/10 split) for testing and training of a model keeping a certain grouping criteria.

Im

Answer 1

comps <- levels(df$companycode)

trn <- sample(comps, length(comps)*0.9)

df.trn <- subset(df, companycode %in% trn)
df.tst <- subset(df, !(companycode %in% trn))

This splits your data so that 90% of companies are in the training set and the rest in the test set.

This does not guarantee that 90% of your rows will be training and 10% test. The rigorous way to achieve this is left as an exercise for the reader. The non-rigorous way would be to repeat the sampling until you get proportions that are roughly correct.