根据唯一值将多个 data.table 列粘贴到单个列中

Question

我有一个如下所示的 data.table：

require("data.table")

dt1 <- data.table(VAR1 = c("Brick","Sand","Concrete","Stone"), VAR2 = c(100,23,76,43), VAR3 = c("Place","Location","Place","Vista"), VAR4 = c("Place","Tree","Wood","Vista"), VAR5 = c("Place","Tree","Wood","Forest"))

我想按以下顺序将命名列（我的真实数据有其他列）粘贴在一起：VAR2、VAR1、VAR3、VAR4 和 VAR5。但是，我有两个条件：

• 不应重复同一行中的值（当值重复时，应保留最后一个条目的列 - 因此在我的示例中，VAR5 中的“位置”将是保留的那个）
• 粘贴时逗号应该是分隔符，VAR2 和 VAR1 之间除外

我的预期输出如下所示：

dt2 <- data.table(VAR6 = c("100 Brick, Place","23 Sand, Location, Tree","76 Concrete, Place, Wood","43 Stone, Vista, Forest"))

Answer 1

我们可以在.SDcols中按顺序选择列后使用do.call(paste，用正则表达式去除重复的单词

dt1[,  .(VAR6 = sub(",", " ", gsub("\\b(\\w+)\\b\\s*,\\s*(?=.*\\1)", "", 
      do.call(paste, c(.SD, sep=",")), perl = TRUE))), 
           .SDcols = names(dt1)[c(2:1, 3:5)]]
#                     VAR6
#1:        100 Brick,Place
#2:  23 Sand,Location,Tree
#3: 76 Concrete,Place,Wood
#4:  43 Stone,Vista,Forest

---

或按行序列分组并执行paste

V6 <- dt1[, sprintf("%s %s, %s", VAR2, VAR1, 
   toString(unique(unlist(.SD)))), 1:nrow(dt1), .SDcols = VAR3:VAR5]$V1
data.table(V6)
#                     V6
#1:         100 Brick, Place
#2:  23 Sand, Location, Tree
#3: 76 Concrete, Place, Wood
#4:  43 Stone, Vista, Forest