从r中的长表创建一个对称矩阵

Question

这是我的数据

df <- data.frame (Var1  <- c("a", "b", "c","d","e","b","c","d","e","c","d","e","d","e","e"),
                  Var2 <- c("a","a","a","a","a","b","b","b","b","c","c","c","d","d","e")
                  pre <- c(1,2,3,4,5,1,6,7,8,1,9,10,1,11,1) )

我想构建一个以var1和var2函数作为rownames和colnames的对称矩阵，矩阵值是r中“pre”中的对应数字，如下所示：

  a b c d e 
a 1 2 3 4 5
b 2 1 6 7 8 
c 3 6 1 9 10
d 4 7 9 1 11
e 5 8 10 11 1

这个貌似很简单的问题，但是google了很多帖子都没有解决，所以特地来问一下，谢谢！

梦影

Answer 1

您可以先获取宽格式的数据。

library(dplyr)
library(tidyr)

mat <- df %>%
  pivot_wider(names_from = Var2, values_from = pre, values_fill = 0) %>%
  column_to_rownames('Var1') %>%
  as.matrix()

mat
#  a b  c  d e
#a 1 0  0  0 0
#b 2 1  0  0 0
#c 3 6  1  0 0
#d 4 7  9  1 0
#e 5 8 10 11 1

由于您有一个对称矩阵，您可以将下三角矩阵复制到上三角。

mat[upper.tri(mat)] <- t(mat)[upper.tri(mat)]
mat

#  a b  c  d  e
#a 1 2  3  4  5
#b 2 1  6  7  8
#c 3 6  1  9 10
#d 4 7  9  1 11
#e 5 8 10 11  1

数据

df <- data.frame (Var1  = c("a", "b", "c","d","e","b","c","d","e","c","d","e","d","e","e"),
                  Var2 = c("a","a","a","a","a","b","b","b","b","c","c","c","d","d","e"),
                  pre = c(1,2,3,4,5,1,6,7,8,1,9,10,1,11,1) )

Answer 2

这是igraph 包的一个选项

g <- graph_from_data_frame(df,directed = FALSE)
E(g)$pre <- df$pre
get.adjacency(g,attr = "pre")

给了

  a b  c  d  e
a 1 2  3  4  5
b 2 1  6  7  8
c 3 6  1  9 10
d 4 7  9  1 11
e 5 8 10 11  1

Answer 3

Base R 解决方案（使用 Ronak 提供的数据）：

# Crosstab: 
mdat <- as.data.frame.matrix(xtabs(pre ~ Var1 + Var2, df))

# Reflect on the diag (thanks @Ronak Shah):
mdat[upper.tri(mdat)] <- t(mdat)[upper.tri(mdat)]

正如@ThomasIsCoding 指出的那样，我们也可以使用这个单线：

xtabs(pre ~ ., unique(rbind(df, cbind(setNames(rev(df[-3]), names(df)[-3]), df[3] ))))

正如@thelatemail 指出的那样，我们还可以：

xtabs(pre ~ ., unique(data.frame(Map(c, df, df[c(2,1,3)]))))

Answer 4

这是一个基本的 R 版本：

df <- data.frame (Var1  = c("a", "b", "c","d","e","b","c","d","e","c","d","e","d","e","e"),
                  Var2 = c("a","a","a","a","a","b","b","b","b","c","c","c","d","d","e"),
                  pre = c(1,2,3,4,5,1,6,7,8,1,9,10,1,11,1))

# Generate new matrix/data frame
mat2 <- matrix(0, length(unique(df$Var1)), length(unique(df$Var2)))

# Name the columns and rows so we can access values
rownames(mat2) <- unique(df$Var1)
colnames(mat2) <- unique(df$Var2)

# Save values into appropriate places into data frame
mat2[as.matrix(df[, 1:2])] <- as.matrix(df[, 3])

# Using upper triangle trick from @Ronak Shah's answer
mat2[upper.tri(mat)] <- t(mat2)[upper.tri(mat2)]

# See results
mat2
#   a b  c  d  e
# a 1 2  3  4  5
# b 2 1  6  7  8
# c 3 6  1  9 10
# d 4 7  9  1 11
# e 5 8 10 11  1