Show only ggpairs upper or lower triangle

Question

The ggpairs function of the Ggally package implements a version of the pairs for ggplot. The chart type displayed in the upper, lower and diagonal triangle of the matrix can be customized with the options upper, lower and diag. So to, for example, display only the upper triangle:

library(GGally)

dados <- iris[, 1:4]

plot.mtx <- ggpairs(dados,
  upper = list(continuous = "points"),
  lower = list(continuous = "blank"),
  diag  = list(continuous = "blankDiag")
)

> plot.mtx

However, rows and columns without charts continue to be displayed. How to have only rows/columns with graphs displayed?

Answer 1

This solution was given by Richard Telford in the OS in English for the lower triangle, I’m expanding and detailing the answer here.

The ggpair creates a list of Plots following a matrix by lines. In the case of 4 variables, we have:

> matrix(1:ncol(dados)^2, nrow = ncol(dados), byrow = TRUE)
    [,1] [,2] [,3] [,4]
[1,]    1    2    3    4
[2,]    5    6    7    8
[3,]    9   10   11   12
[4,]   13   14   15   16

> length(plot.mtx$plots)
[1] 16

> plot.mtx$nrow; plot.mtx$ncol
[1] 4
[1] 4

So, in case you display the upper triangle, we need to cut the Plots first column and diagonal. In the case of the lower triangle, last line and diagonal. Between these steps, it is also necessary to update row and column numbers (stored in proper elements within the ggpairs list), as well as labels:

ggpairs_upper <- function(g) {
  g$plots <- g$plots[-seq(length(g$plots)-g$nrow+1, length(g$plots))]
  g$yAxisLabels <- g$yAxisLabels[-g$nrow]
  g$nrow <- g$nrow -1
  g$plots <- g$plots[-seq(1, g$nrow*g$ncol, by = g$ncol+1)]
  g$xAxisLabels <- g$xAxisLabels[-1]
  g$ncol <- g$ncol - 1
  g
}

ggpairs_lower <- function(g) {
  g$plots <- g$plots[-(1:g$nrow)]
  g$yAxisLabels <- g$yAxisLabels[-1]
  g$nrow <- g$nrow -1
  g$plots <- g$plots[-(seq(g$ncol, length(g$plots), by = g$ncol))]
  g$xAxisLabels <- g$xAxisLabels[-g$ncol]
  g$ncol <- g$ncol - 1
  g
}

> ggpairs_upper(plot.mtx)