字符串拆分的第一个条目 [英] First entry from string split

问题描述

我有一个 people$food 列，其中包含诸如 chocolate 或 apple-orange-strawberry 之类的条目.

I've got a column people$food that has entries like chocolate or apple-orange-strawberry.

我想通过 - 拆分 people$food 并从拆分中获取第一个条目.

I want to split people$food by - and get the first entry from the split.

在 python 中，解决方案是 food.split('-')[0]，但我找不到 R 的等价物.

In python, the solution would be food.split('-')[0], but I can't find an equivalent for R.

推荐答案

如果您需要从每个拆分中提取第一个(或 nth)个条目，请使用:

If you need to extract the first (or nth) entry from each split, use:

word <- c('apple-orange-strawberry','chocolate')

sapply(strsplit(word,"-"), `[`, 1)
#[1] "apple"     "chocolate"

或者更快更明确:

vapply(strsplit(word,"-"), `[`, 1, FUN.VALUE=character(1))
#[1] "apple"     "chocolate"

这两部分代码都可以很好地处理选择拆分列表中的任何一个值，并将处理超出范围的情况:

Both bits of code will cope well with selecting whichever value in the split list, and will deal with cases that are outside the range:

vapply(strsplit(word,"-"), `[`, 2, FUN.VALUE=character(1))
#[1] "orange" NA  

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