data.table：如何对一个键处的两个（数字）值进行二进制搜索：包括示例 [英] data.table: How to do binary search for two (numeric) values at one key: example included

问题描述

示例数据：

library(data.table)
DT <- data.table(a = c(1, 3, 5, 9, 15), 
                 b = c("a", "c", "d", "e", "f"))

我想得到两行，即 a == 3 | a == 9 ，即

# a b
# 3 c
# 9 e

我知道是否这样做： DT [，a： = as.character（a）] 然后 setkey（DT，a）和 DT [c（ 3， 9）] ，我可以得到想要的结果。但是我想知道，是否还有其他方法可以执行这种二进制搜索而无需预先将 a 更改为字符？

I know if I do: DT[, a:=as.character(a)] then setkey(DT, a) and DT[c("3", "9")], I can get the wanted result. But I would like to know, if there are other methods to do this kind of binary search without changing a to character in advance?

推荐答案

您无需将其转换为字符向量（尽管整数会更有意义）

You don't need to convert it into a character vector (although integer would make more sense)

 DT <- data.table(a = c(1, 3, 5, 9, 15), b = c("a", "c", "d", "e", "f"))
 setkey(DT, a)
 DT[J(c(3, 9))]

此外，如果您使用的是CRAN中的最新版本，则第二次在i中使用a将自动使用二进制搜索

Moreover, if you have the latest version in CRAN, the second time you use a in i will automatically uses binary search

这篇关于data.table：如何对一个键处的两个（数字）值进行二进制搜索：包括示例的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！