How do I add significance asterisks next to my values in a correlation matrix heat map? - heatmap

Question

I found this code online at http://www.sthda.com/english/wiki/ggplot2-quick-correlation-matrix-heatmap-r-software-and-data-visualization
It provides instructions for how to create a correlation matrix heat map and it works well. However, I was wondering how to get little stars * next to the values in the matrix that are significant. How would I go about doing that. Any help is greatly appreciated!!
mydata <- mtcars[, c(1,3,4,5,6,7)]
head(mydata)
cormat <- round(cor(mydata),2)
head(cormat)
library(reshape2)
melted_cormat <- melt(cormat)
head(melted_cormat)
library(ggplot2)
ggplot(data = melted_cormat, aes(x=Var1, y=Var2, fill=value)) +
geom_tile()
# Get lower triangle of the correlation matrix
get_lower_tri<-function(cormat){
cormat[upper.tri(cormat)] <- NA
return(cormat)
}
# Get upper triangle of the correlation matrix
get_upper_tri <- function(cormat){
cormat[lower.tri(cormat)]<- NA
return(cormat)
}
upper_tri <- get_upper_tri(cormat)
# Melt the correlation matrix
library(reshape2)
melted_cormat <- melt(upper_tri, na.rm = TRUE)
# Heatmap
library(ggplot2)
ggplot(data = melted_cormat, aes(Var2, Var1, fill = value))+
geom_tile(color = "white")+
scale_fill_gradient2(low = "blue", high = "red", mid = "white",
midpoint = 0, limit = c(-1,1), space = "Lab",
name="Pearson\nCorrelation") +
theme_minimal()+
theme(axis.text.x = element_text(angle = 45, vjust = 1,
size = 12, hjust = 1))+
coord_fixed()
reorder_cormat <- function(cormat){
# Use correlation between variables as distance
dd <- as.dist((1-cormat)/2)
hc <- hclust(dd)
cormat <-cormat[hc$order, hc$order]
}
# Reorder the correlation matrix
cormat <- reorder_cormat(cormat)
upper_tri <- get_upper_tri(cormat)
# Melt the correlation matrix
melted_cormat <- melt(upper_tri, na.rm = TRUE)
# Create a ggheatmap
ggheatmap <- ggplot(melted_cormat, aes(Var2, Var1, fill = value))+
geom_tile(color = "white")+
scale_fill_gradient2(low = "blue", high = "red", mid = "white",
midpoint = 0, limit = c(-1,1), space = "Lab",
name="Pearson\nCorrelation") +
theme_minimal()+ # minimal theme
theme(axis.text.x = element_text(angle = 45, vjust = 1,
size = 12, hjust = 1))+
coord_fixed()
# Print the heatmap
print(ggheatmap)
ggheatmap +
geom_text(aes(Var2, Var1, label = value), color = "black", size = 4) +
theme(
axis.title.x = element_blank(),
axis.title.y = element_blank(),
panel.grid.major = element_blank(),
panel.border = element_blank(),
panel.background = element_blank(),
axis.ticks = element_blank(),
legend.justification = c(1, 0),
legend.position = c(0.6, 0.7),
legend.direction = "horizontal")+
guides(fill = guide_colorbar(barwidth = 7, barheight = 1,
title.position = "top", title.hjust = 0.5))

Answer 1

cor() doesn't show the significance level, you may have to use rcorr() from Hmisc package
This is quite similar to what you want (the graphic output is not so nice though)
library(ggplot2)
library(reshape2)
library(Hmisc)
library(stats)
abbreviateSTR <- function(value, prefix){ # format string more concisely
lst = c()
for (item in value) {
if (is.nan(item) || is.na(item)) { # if item is NaN return empty string
lst <- c(lst, '')
next
}
item <- round(item, 2) # round to two digits
if (item == 0) { # if rounding results in 0 clarify
item = '<.01'
}
item <- as.character(item)
item <- sub("(^[0])+", "", item) # remove leading 0: 0.05 -> .05
item <- sub("(^-[0])+", "-", item) # remove leading -0: -0.05 -> -.05
lst <- c(lst, paste(prefix, item, sep = ""))
}
return(lst)
}
d <- mtcars
cormatrix = rcorr(as.matrix(d), type='spearman')
cordata = melt(cormatrix$r)
cordata$labelr = abbreviateSTR(melt(cormatrix$r)$value, 'r')
cordata$labelP = abbreviateSTR(melt(cormatrix$P)$value, 'P')
cordata$label = paste(cordata$labelr, "\n",
cordata$labelP, sep = "")
cordata$strike = ""
cordata$strike[cormatrix$P > 0.05] = "X"
txtsize <- par('din')[2] / 2
ggplot(cordata, aes(x=Var1, y=Var2, fill=value)) + geom_tile() +
theme(axis.text.x = element_text(angle=90, hjust=TRUE)) +
xlab("") + ylab("") +
geom_text(label=cordata$label, size=txtsize) +
geom_text(label=cordata$strike, size=txtsize * 4, color="red", alpha=0.4)
Source

Answer 2

difference_p is the P_value of correlation matrix,
ax5 draws the sns.heatmap and return as ax5
data=correlation_p
for y in range(data.shape[0]):
for x in range(data.shape[1]):
if data[y,x]<0.1:
ax4.text(x + 0.5, y + 0.5, '-',size=48,
horizontalalignment='center',
verticalalignment='center',
)