配对列和系数中R中的相关矩阵

Question

I have a dataframe that has three variables: a, b, c. The first two columns in the data set are the pairing of two of the variables for all possible combinations and the third is the correlation between them. Shown below.

> var1 <- c("a","a","b")
> var2 <- c("b","c","c")
> r <- c(.55,.25,.75)
> as.data.frame(cbind(var1,var2,r))
  var1 var2    r
1    a    b  0.55
2    a    c  0.25
3    b    c  0.75

My question is whether it is possible to turn this dataframe containing the correlations into a correlation matrix object in R? I also want to use some of R's plotting and graphing functions.

Ultimately what I want is a matrix that looks like this

  a    b    c
a 1   .55  .25

b .55  1   .25

c .25  .75  .75

Answer 1

Try this:

vars <- unique(c(var1, var2))
df <- cbind.data.frame(var1,var2,r)
cor.df <- expand.grid(vars, vars)
cor.df <- rbind(merge(cor.df, df, by.x=c('Var1', 'Var2'), by.y=c('var1', 'var2')),
                merge(cor.df, df, by.x=c('Var2', 'Var1'), by.y=c('var1', 'var2')),
                data.frame(Var1=vars, Var2=vars, r=1))
library(reshape2)
cor.mat <- dcast(cor.df, Var1~Var2, value.var='r')
rownames(cor.mat) <- cor.mat[,1]
cor.mat <- as.matrix(cor.mat[-1])
cor.mat
#      a    b    c
# a 1.00 0.55 0.25
# b 0.55 1.00 0.75
# c 0.25 0.75 1.00

# plot the correlation matrix
library(ggplot2)
ggplot(data = cor.df, aes(x=Var1, y=Var2, fill=r)) + 
  geom_tile()

Answer 2

Obviously you have the upper triangular and lower triangular parts of your correlation matrix (provided by r ) and you do not need the data.frame for your purpose. Supplying the lower and upper triangle for a matrix which elements are 1 is enough.

var <- unique(c(var1,var2))
corr <- matrix(1,nrow=length(r),ncol=length(r)) # a matrix with 1s
corr[lower.tri(corr,diag = FALSE)] <- r # lower triangular matrix to be r
corr[upper.tri(corr,diag = FALSE)] <- r # upper triangular matrix to be r 
corr <- as.data.frame(corr) # formatting
row.names(corr) <- var # row names
colnames(corr) <- var # column names

Package corrplot has a function corrplot perfect for plotting correlation matrix with different options (see the argument method ). Here is an example:

library(corrplot)
corrplot(as.matrix(corr),method="circle")