Function prepare_histogram_by 

pub fn prepare_histogram_by(
    lf: &LazyFrame,
    column: &str,
    bins: usize,
    range: ValueRange,
    share: bool,
    color: Option<ColorSplit<'_>>,
    sampling: &ChartSampling,
) -> Result<HistogramData>

Prepare a histogram of column, split by color into groups on the same bins when given. With share, a bin is its share of its group’s rows (of every row, unsplit), so groups of different sizes compare. The range is the whole column’s, so every group is clipped alike.