Subset points using a grid-based system, to avoid unnecessary rendering when plotting.
Arguments
- X
A numeric vector of x-coordinates for all points.
- Y
A numeric vector of y-coordinates for all points, of the same length as
X.- resolution
A positive integer specifying the number of bins on each axis of the grid.
Alternatively, if
groupingis specified, this may be a named integer vector containing the number of bins to be used for each level.- grouping
A character vector of length equal to
Xspecifying the group to which each point is assigned. By default, all points belong to the same group.
Details
This function will define a grid of the specified resolution across the plot. Each point is allocated to a grid location (i.e., pair of bins on the x- and y-axes). If multiple points are allocated to a given location, only the last/right-most point is retained. This mimics the fact that plotting will overwrite earlier points with later points. In this manner, we can avoid unnecessary rendering of earlier points that would not show up anyway.
If grouping is specified, redundant points are only identified within each unique level.
The resolution of downsampling within each level can be varied by passing an integer vector to resolution.
This can be useful for tuning the downsampling when points differ in importance,
e.g., in a MA plot, points corresponding to non-DE genes can be aggressively downsampled
while points corresponding to DE genes should generally be retained.
For plots where X and Y are originally categorical, use the jittered versions as input to this function.
Examples
X <- rnorm(100000)
Y <- X + rnorm(100000)
summary(subsetPointsByGrid(X, Y, resolution=100))
#> Mode FALSE TRUE
#> logical 96693 3307
summary(subsetPointsByGrid(X, Y, resolution=200))
#> Mode FALSE TRUE
#> logical 90026 9974
summary(subsetPointsByGrid(X, Y, resolution=1000))
#> Mode FALSE TRUE
#> logical 31236 68764