data.table中 between 与 inrange的区别

问题来源于一片博客data.table 与 dplyr 的区别

查阅到 between vs inrange in data.table

• 官方说明书
• between is equivalent to x >= lower & x <= upper when incbounds=TRUE, or x > lower & y < upper when FALSE, It is set to TRUE by default for infix notations. With a caveat that NA in lower or upper are taken as a missing bound and return TRUE not NA.
• inrange checks whether each value in x is in between any of the intervals provided in lower,upper.

between(x, lower, upper, incbounds=TRUE)
x %between% y
inrange(x, lower, upper, incbounds=TRUE)
x %inrange% y

> library(data.table)
> X = data.table(a=1:5, b=6:10, c=c(5:1))
> X
   a  b c
1: 1  6 5
2: 2  7 4
3: 3  8 3
4: 4  9 2
5: 5 10 1

> X[a %between% list(c, b)]
   a  b c
1: 3  8 3
2: 4  9 2
3: 5 10 1

> X[a %between% list(b, c)]
Empty data.table (0 rows) of 3 cols: a,b,c

> X[a %inrange% list(c, b)]
   a  b c
1: 1  6 5
2: 2  7 4
3: 3  8 3
4: 4  9 2
5: 5 10 1

> X[a %inrange% list(b, c)]
Empty data.table (0 rows) of 3 cols: a,b,c

• 从上面可以看出X[a %between% list(c, b)]中%between%表示的是Cn ≤ An ≤ Bn的行
• 而 X[a %inrange% list(c, b)] 表示是：假设在列c中的最小值为Cmin, 列b中的最大值为Bmax，那么结果就是符合Cmin ≤ a ≤ Bmax的行，其实不难理解，我们可以看到当list(c, b)变为list(b, c)时候是没有结果输出的。