相关疑难解决方法(0)

我试图在R中的data.table中存在重复键时理解J()查找的逻辑.

这是我尝试过的一个小实验:

library(data.table)
options(stringsAsFactors = FALSE)

x <- data.table(keyVar = c("a", "b", "c", "c"),
            value  = c(  1,   2,   3,   4))
setkey(x, keyVar)

y1 <- data.frame(name = c("d", "c", "a"))
x[J(y1$name), ]
## OK

y2 <- data.frame(name = c("d", "c", "a", "b"))
x[J(y2$name), ]
## Error: see below

x2 <- data.table(keyVar = c("a", "b", "c"),
                 value  = c(  1,   2,   3))
setkey(x2, keyVar)
x2[J(y2$name), ]
## OK

我得到的错误消息是:

Error in vecseq(f__, len__, if (allow.cartesian) NULL else as.integer(max(nrow(x),  :
Join results …