如何将data.frame反熔铸为矩阵？附具体实例需求

现有如下R数据框：

sources <- c("a", "b", "c", "a", "a", "b")
targets <- c("f", "v", "w", "a", "b", "c")
values <- c(12, 34, 56, 3, 76, 35)
df <- data.frame(sources, targets, values)

数据框内容：

sources targets values
1       a       f     12
2       b       v     34
3       c       w     56
4       a       a      3
5       a       b     76
6       b       c     35

需要将其转换为以sources取值为行名、targets取值为列名的矩阵，交叉单元格填充对应values值，无对应值的位置填0，最终得到如下3×6的矩阵：

f  v  w  a  b  c
a  12  0  0  3  76  0
b   0 34  0  0   0 35
c   0  0 56  0   0  0

方法1：使用tidyr包的pivot_wider #

# 首次使用需安装包
install.packages("tidyr")
library(tidyr)

# 重塑数据并转换为矩阵
result_df <- pivot_wider(df, 
                         id_cols = sources, 
                         names_from = targets, 
                         values_from = values, 
                         values_fill = 0)
result_matrix <- as.matrix(result_df[,-1])
rownames(result_matrix) <- result_df$sources
# 调整列顺序匹配示例要求
result_matrix <- result_matrix[, c("f", "v", "w", "a", "b", "c")]

print(result_matrix)

方法2：使用基础R的xtabs函数 #

无需额外安装包，基础R自带函数即可实现：

# 生成交叉表并转为矩阵
result_matrix <- as.matrix(xtabs(values ~ sources + targets, data = df))
# 调整列顺序匹配示例
result_matrix <- result_matrix[, c("f", "v", "w", "a", "b", "c")]

print(result_matrix)

方法3：使用reshape2包的dcast #

# 首次使用需安装包
install.packages("reshape2")
library(reshape2)

# 重塑数据并转换为矩阵
result_df <- dcast(df, sources ~ targets, value.var = "values", fill = 0)
result_matrix <- as.matrix(result_df[,-1])
rownames(result_matrix) <- result_df$sources
result_matrix <- result_matrix[, c("f", "v", "w", "a", "b", "c")]

print(result_matrix)

内容的提问来源于stack exchange，提问作者Yulia Kentieva