grep在固定= T在R的字符串的开始？ [英] grep at the beginning of the string with fixed =T in R?

问题描述

如何grep with fixed = T ，但只在字符串的开头？

  grep（a。，c（ab，cac，sss，ca.f），fixed = T）
＃1 4 
  

我只想得到第一个匹配项。

谢谢。

]

解决方案

如果要匹配字符串（字符串2）开始处的确切字符串（字符串1），则只需将字符串2的子集相同即可长度为字符串1并使用==，应该相当快。

How to grep with fixed=T, but only at the beginning of the string?

grep("a.", c("a.b", "cac", "sss", "ca.f"), fixed = T)
# 1 4

I would like to get only the first occurrence. [Edit: the string to match is not known in advance, and can be anything. "a." is just for the sake of example]

Thanks.

[Edit: I sort of solved it now, but any other ideas are highly welcome. I will accept as an answer any alternative solution.

s <- "a."
res <- grep(s, c("a.b", "cac", "sss", "ca.f"), fixed = T, value = T)
res[substring(res, 1, nchar(s)) == s]

]

解决方案

If you want to match an exact string (string 1) at the beginning of the string (string 2), then just subset your string 2 to be the same length as string 1 and use ==, should be fairly fast.

这篇关于grep在固定= T在R的字符串的开始？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！