Converting R data.frame to matrix with levels of two factors as row and column names of the matrix

Question

I want to converting R data.frame to matrix with levels of two factors as row and column names of the matrix. Here is a MWE. It is a lot of code to get the desired result and there might be more compact code for this purpose.

set.seed(12345)
A <- c("A1", "A2")
B <- c("B1", "B2", "B3")
Y <- runif(n=6, min=100, max=1000)
df <- data.frame(expand.grid(A=A, B=B), Y)
df

#    A  B        Y
# 1 A1 B1 748.8135
# 2 A2 B1 888.1959
# 3 A1 B2 784.8841
# 4 A2 B2 897.5121
# 5 A1 B3 510.8329
# 6 A2 B3 249.7346

library(tidyr)
df1 <- spread(data = df, key = A, value = Y, fill = NA, convert = FALSE, drop = TRUE)
df1

#   B       A1       A2
# 1 B1 748.8135 888.1959
# 2 B2 784.8841 897.5121
# 3 B3 510.8329 249.7346


m1 <- as.matrix(df1[,-1])
rownames(m1) <- df1[ ,1]
m1

#     A1       A2
# B1 748.8135 888.1959
# B2 784.8841 897.5121
# B3 510.8329 249.7346

Answer 1

acast可以使用包中的函数来完成reshape2。

df4 <- reshape2::acast(df, B ~ A, value.var="Y")
df4

#       A1       A2
# B1 748.8135 888.1959
# B2 784.8841 897.5121
# B3 510.8329 249.7346