cowplot (version 1.1.3)

align_margin: Align multiple plots along a specified margin

Description

The function aligns the dimensions of multiple plots along a specified axis, and is solely a helper function for align_plots() to reduce redundancy. Each element of the sizes list corresponds to the dimensions of a plot being aligned. They should be vectors created from calls to grob$heights or grob$widths depending on whether you are aligning vertically or horizontally. The list of dimensions is generated automatically by the align_plots() function, but see examples. If the same number of elements exist for all plots for the specified margin, the function will align individual elements on the margin. Otherwise, it aligns the plot by adding white space to plot margins so that all margins have the same dimensions.

Usage

align_margin(sizes, margin_to_align, greedy = TRUE)

Arguments

sizes

list of dimensions for each plot being aligned. Each element of list obtained by a call to grob$heights or grob$widths (see example).

margin_to_align

string either "first" or "last" for which part of plot area should be aligned. If vertically aligning, "first" aligns left margin and "last" aligns right margin. If horizontally aligning "first" aligns top margin and "last" aligns bottom margin.

greedy

if TRUE, alignment is always achieved by adjusting the most extreme margin; if FALSE, and the number of dimensions for each plot are the same, then all dimensions are jointly adjusted.

Examples

library(ggplot2)

# Example for how to utilize, though align_plots() does this internally and automatically
df <- data.frame(
  x = 1:10, y1 = 1:10, y2 = (1:10)^2, y3 = (1:10)^3
)

p1 <- ggplot(df, aes(x, y1)) + geom_point()
p2 <- ggplot(df, aes(x, y2)) + geom_point()
p3 <- ggplot(df, aes(x, y3)) + geom_point()
plots <- list(p1, p2, p3)
grobs <- lapply(plots, as_grob)
plot_widths <- lapply(grobs, function(x) {x$widths})
# Aligning the left margins of all plots
aligned_widths <- align_margin(plot_widths, "first")
# Aligning the right margins of all plots as well
aligned_widths <- align_margin(aligned_widths, "last")
# Setting the dimensions of plots to the aligned dimensions
for (i in seq_along(plots)) {
  grobs[[i]]$widths <- aligned_widths[[i]]
}
# Draw aligned plots
plot_grid(plotlist = grobs, ncol = 1)