[R] sample equal number of cases per class

[ollestrat]

Dear community

I have a dataframe and want to split it into a learn and a test partition.
However the learnset should be balanced, i.e. each class should have the
same number of cases. I tried and searched a lot, without success so far.
Maybe you can help?

Some example code
*# generate example data
df <- data.frame(class = as.factor(sample(1:3, 20, replace = T)), var1 =
rnorm(20,3), var2 = rnorm(20,6))
summary(df)

# split into learn and test sets using the caret package
require(caret)
ind <- createDataPartition(df$class, p=.8, list = F, times = 1)

# The problem is here: class sizes are not equal)
learnset <- df[ind,]
summary(learnset)*

Version info:
/> R.Version()
$platform
[1] "x86_64-pc-mingw32"
$arch
[1] "x86_64"
$os
[1] "mingw32"
$system
[1] "x86_64, mingw32"
$major
[1] "2"
$minor
[1] "15.1"/



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