Decrease the observations in a task or a ResampleInstance
to a given percentage of observations.
downsample(obj, perc = 1, stratify = FALSE)([data.frame| [Task] | [ResampleInstance]). Same type asobj`.
(Task | ResampleInstance)
Input data or a ResampleInstance.
(numeric(1))
Percentage from (0, 1).
Default is 1.
(logical(1))
Only for classification:
Should the downsampled data be stratified according to the target classes?
Default is FALSE.
makeResampleInstance
Other downsample: 
makeDownsampleWrapper()