Quantile-based cut points for coplots

This helper wraps quantile to create well-spaced cut points for conditioning plots. When intervals = TRUE the lower boundary is nudged down so that cut() treats the minimum value as a valid observation.

The output can be passed directly into the breaks argument of the cut function for creating groups for coplots.

Usage

quantile_pts(object, groups, intervals = FALSE)

Arguments

object

Numeric vector of predictor values.

groups

Number of quantile points (or intervals) to compute.

intervals

Logical indicating whether to return interval boundaries suitable for cut() (length groups + 1) or the interior quantile points (length groups).

Value

Numeric vector of quantile points. When intervals = TRUE the result is strictly increasing and can be supplied to cut() to produce groups balanced strata.

See also

cut

Examples

data(Boston, package = "MASS")
rfsrc_boston <- randomForestSRC::rfsrc(medv ~ ., Boston)

# To create 6 intervals, we want 7 points.
# quantile_pts will find balanced intervals
rm_pts <- quantile_pts(rfsrc_boston$xvar$rm, groups = 6, intervals = TRUE)

# Use cut to create the intervals
rm_grp <- cut(rfsrc_boston$xvar$rm, breaks = rm_pts)

summary(rm_grp)
#> (3.56,5.76] (5.76,5.99] (5.99,6.21] (6.21,6.44] (6.44,6.85] (6.85,8.78] 
#>          85          84          84          85          84          84