R加入data.table

Question

我正在尝试在 x$val >= y$start & x$val

data.table 确实有不等式连接，但我一生都无法弄清楚语法是如何工作的。看到这个结果：

x <- data.table(val = c(1:5), id = "a")
y <- data.table(start = c(1:5), end = c(11:15), id= "a")

x[y, on=c("val>=start","val<=end"),
  .(start, val, end)]

    start val end
 1:     1   1  11
 2:     1   1  11
 3:     1   1  11
 4:     1   1  11
 5:     1   1  11
 6:     2   2  12
 7:     2   2  12
 8:     2   2  12
 9:     2   2  12
10:     3   3  13
11:     3   3  13
12:     3   3  13
13:     4   4  14
14:     4   4  14
15:     5   5  15

为了展示我期望得到的结果，这里是 dplyr 产生的：

x <- data.table(val = c(1:5), id = "a")
y <- data.table(start = c(1:5), end = c(11:15), id= "a")

x %>% 
  inner_join(y) %>% 
  filter(val >= start & val <= end)

   val   id start end
1    1    a     1  11
2    2    a     1  11
3    2    a     2  12
4    3    a     1  11
5    3    a     2  12
6    3    a     3  13
7    4    a     1  11
8    4    a     2  12
9    4    a     3  13
10   4    a     4  14
11   5    a     1  11
12   5    a     2  12
13   5    a     3  13
14   5    a     4  14
15   5    a     5  15

谁能解释我在 data.table 语法中缺少什么？

Answer 1

您需要从左表中选择val列，前缀为（x.）；更多信息请见this answer：

x[y, on=.(val >= start, val <= end), .(val = x.val, id, start, end)][order(val)]
 #                                           ^^
 #   val id start end
 #1:   1  a     1  11
 #2:   2  a     1  11
 #3:   2  a     2  12
 #4:   3  a     1  11
 #5:   3  a     2  12
 #6:   3  a     3  13
 #7:   4  a     1  11
 #8:   4  a     2  12
 #9:   4  a     3  13
#10:   4  a     4  14
#11:   5  a     1  11
#12:   5  a     2  12
#13:   5  a     3  13
#14:   5  a     4  14
#15:   5  a     5  15