heatmap with values (ggplot2)

Question

I've seen heatmaps with values made in various R graphics systems including lattice and base like this:

I tend to use ggplot2 a bit and would like to be able to make a heatmap with the corresponding cell values plotted. Here's the heat map and an attempt using geom_text:

library(reshape2, ggplot2) dat <- matrix(rnorm(100, 3, 1), ncol=10) names(dat) <- paste("X", 1:10) dat2 <- melt(dat, id.var = "X1") p1 <- ggplot(dat2, aes(as.factor(Var1), Var2, group=Var2)) +     geom_tile(aes(fill = value)) +     scale_fill_gradient(low = "white", high = "red")  p1  #attempt labs <- c(apply(round(dat[, -2], 1), 2, as.character)) p1 +  geom_text(aes(label=labs), size=1) 

Normally I can figure out the x and y values to pass but I don't know in this case since this info isn't stored in the data set. How can I place the text on the heatmap?

Answer 1

This has been updated to conform to tidyverse principles and improve poor use of ggplot2

Per SlowLeraner's comment I was easily able to do this:

library(tidyverse)  ## make data dat <- matrix(rnorm(100, 3, 1), ncol=10)  ## reshape data (tidy/tall form) dat2 <- dat %>%     tbl_df() %>%     rownames_to_column('Var1') %>%     gather(Var2, value, -Var1) %>%     mutate(         Var1 = factor(Var1, levels=1:10),         Var2 = factor(gsub("V", "", Var2), levels=1:10)     )  ## plot data ggplot(dat2, aes(Var1, Var2)) +     geom_tile(aes(fill = value)) +      geom_text(aes(label = round(value, 1))) +     scale_fill_gradient(low = "white", high = "red")