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rcorrelationggallyggpairs

Adding p-value and r-value in separate lines in correlogram using ggpairs in R

I am trying to plot a correlation matrix using the ggpairs function in the GGally R package. By default it displays the correlation coefficient in digits and adds stars next to it to represent the p-value. However I would like to have the correlation coefficient and the p-value both in digits upto two decimals, one below the other.

e.g. r = 0.84
     p = 0.01

Here's the data:

> dput(df)
structure(list(A = c(7.4434, 8.1305, 8.8554, 7.6841, 6.9656, 
8.2225, 7.7836, 6.8234, 8.6265, 8.3475, 8.1828), B = c(5.4939, 
6.8466, 6.796, 6.2022, 5.0935, 7.0202, 5.4479, 4.9634, 6.6522, 
6.451, 7.3865), C = c(10.1219, 10.863, 10.6, 10.7336, 9.8241, 
10.6802, 10.2687, 9.2575, 10.581, 10.7611, 10.6775), D = c(6.3524, 
4.5371, 3.4795, 3.8661, 7.5537, 3.7855, 4.3958, 8.1428, 3.7458, 
4.1419, 3.6338)), row.names = c(NA, -11L), class = c("tbl_df", 
"tbl", "data.frame"))

and this is what I have tried so far:

library(GGally) 

ggpairs(data = df,
    upper = list(continuous = wrap("cor", method = "pearson", size = 6, color = "black")), 
    lower = list(continuous = wrap("smooth", color = "firebrick")),
    diag = list(continuous = wrap("densityDiag", fill = "slategray3")))

enter image description here

Solution

  • One option to achieve your desired result would be to use a customized function for which I adapted the source code of ggally_cor:

    library(GGally)

my_ggally_cor <- function(data,
                          mapping,
                          ...) {
  args <- list(...)
  ggally_statistic(
    data,
    mapping,
    title = NULL,
    sep = NULL,
    text_fn = function(x, y) {
      corObj <- stats::cor.test(x, y,
        method = args$method,
        use = args$use
      )
      cor_est <- as.numeric(corObj$estimate)
      p_est <- as.numeric(corObj$p.value)

      cor_txt <- formatC(cor_est, digits = args$digits, format = "f")
      p_txt <- formatC(p_est, digits = args$digits, format = "f")
      paste0("r = ", cor_txt, "\n", "p = ", p_txt)
    }
  )
}

ggpairs(
  data = df,
  upper = list(continuous = wrap(
    my_ggally_cor,
    method = "pearson", digits = 2,
    size = 6, color = "black"
  )),
  lower = list(continuous = wrap("smooth", color = "firebrick")),
  diag = list(continuous = wrap("densityDiag", fill = "slategray3"))
)