Question

我有以下data.tables：

Comparison <- data.table(code = c("AAA", "BBB"),
                         elem1 = c(1, 2),
                         elem2 = c(4, 4))

DT <- data.table(A = c("AAA", "AAA", "AAA", "AAA"),
                 B = c("BBB", "BBB", "BBB", "BBB"),
                 C = c(1, 2, 3, 4))

现在，我想根据Comparison和DT列的比较添加新列。以下命令生成预期输出：

DT[, newCol := {ifelse( abs(C - Comparison[code == "AAA", elem2]) == 0, "0", "1")}]

Output:

     A   B C newCol
1: AAA BBB 1      1
2: AAA BBB 2      1
3: AAA BBB 3      1
4: AAA BBB 4      0

但是，如果不是对列A的列值进行硬编码，而是使用列本身：

DT[, newCol := {ifelse( abs(C - Comparison[code == A, elem2]) > 0, "0", "1")}]

它输出以下错误，我不知道该如何避免：

Error in `[.data.table`(Comparison, code == A, elem2) : 
  RHS of == is length 4 which is not 1 or nrow (2). For robustness, no recycling is allowed (other than of length 1 RHS). Consider %in% instead.

在我看来，该操作没有对A中DT的{{1}}列的元素进行矢量化，我真的不明白为什么，因为列的元素Comparison被正确使用（即它单独使用C的元素，但不使用C的元素。我怎么能进行这种比较？

非常感谢任何帮助。

Answer 1

一种解决方案是进行数据合并。

require(data.table)

Comparison <- data.table(code = c("AAA", "BBB"),
                         elem1 = c(1, 2),
                         elem2 = c(4, 4))
Comparison

DT <- data.table(A = c("AAA", "AAA", "AAA", "AAA"),
                 B = c("BBB", "BBB", "BBB", "BBB"),
                 C = c(1, 2, 3, 4))
DT

tmp <- merge(DT, Comparison, by.x = "A", by.y = "code")
tmp[, newCol := as.character(as.integer(C != elem2))]
tmp

Answer 2

我们可以将join与on

一起使用

DT[Comparison, newCol := as.integer(C != elem2), on = c("A" = "code"), nomatch = 0]
DT
#     A   B C newCol
#1: AAA BBB 1      1
#2: AAA BBB 2      1
#3: AAA BBB 3      1
#4: AAA BBB 4      0

Answer 3

如果您阅读错误消息，请说明Consider %in% instead.

确实，将==替换为%in%，无需使用join或merge即可。

DT[, newCol := {ifelse( abs(C - Comparison[code %in% A, elem2]) = 0, "0", "1")}

DT

#     A   B C newCol
#1: AAA BBB 1      1
#2: AAA BBB 2      1
#3: AAA BBB 3      1
#4: AAA BBB 4      0

另一个data.table中的data.table引用列，名称为

3 个答案: