如何选择R data.table行基于子字符串匹配（一个类似于SQL） [英] How to select R data.table rows based on substring match (a la SQL like)

问题描述

我有一个data.table与一个字符列，并希望只选择其中包含子字符串的那些行。相当于SQL WHERE x LIKE'％substring％'

I have a data.table with a character column, and want to select only those rows that contain a substring in it. Equivalent to SQL WHERE x LIKE '%substring%'

例如

> Months = data.table(Name = month.name, Number = 1:12)
> Months["mb" %in% Name]
Empty data.table (0 rows) of 2 cols: Name,Number

如何只选择Name包含mb的行？

How would I select only the rows where Name contains "mb"?

推荐答案

data.table 有像函数。

Months[like(Name,"mb")]
        Name Number
1: September      9
2:  November     11
3:  December     12

或者，％like％看起来更好：

> Months[Name %like% "mb"]
    Name Number
1: September      9
2:  November     11
3:  December     12

请注意，％like％和 like c $ c>使用 grepl （返回逻辑向量）而不是 grep （返回整数位置）。因此，它可以与其他逻辑条件组合：

Note that %like% and like() use grepl (returns logical vector) rather than grep (returns integer locations). That's so it can be combined with other logical conditions :

> Months[Number<12 & Name %like% "mb"]
        Name Number
1: September      9
2:  November     11

，你会得到正则表达式搜索的力量（不仅仅是％或*通配符）。

and you get the power of regular expression search (not just % or * wildcard), too.

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