grep {base} 系列

grep 系列返回符合正则条件的元素在向量中位置、本身、或者逻辑值。

  1. grep("a",c("a1","a2","b1","b2"))
  2. ## [1] 1 2
  4. grep("a",c("a1","a2","b1","b2"),value = T)
  5. ## [1] "a1" "a2"
  7. grepl("a",c("a1","a2","b1","b2"))
  8. ## [1]  TRUE  TRUE FALSE FALSE

sub 替换第一次匹配的元素，gsub是贪婪模式，替换所有匹配到的。

  1. sub("a",replacement = "A",x=c("a1a","a2","b1","b2"))
  2. ## [1] "A1a" "A2"  "b1"  "b2" 
  4. gsub("a",replacement = "A",x=c("a1a","a2","b1","b2"))
  5. ## [1] "A1A" "A2"  "b1"  "b2"

regexpr 和 gregexpr 不是返回在向量中的位置，而是分别返回在每个元素中的位置。

  1. regexpr("a",c("1aa","12aba","123abca"))
  2. ## [1] 2 3 4
  3. ## attr(,"match.length")
  4. ## [1] 1 1 1
  5. ## attr(,"index.type")
  6. ## [1] "chars"
  7. ## attr(,"useBytes")
  8. ## [1] TRUE
  10. gregexpr("a",c("1aa","12aba","123abca"))
  11. # [[1]]
  12. # [1] 2 3
  13. # attr(,"match.length")
  14. # [1] 1 1
  15. # attr(,"index.type")
  16. # [1] "chars"
  17. # attr(,"useBytes")
  18. # [1] TRUE
  19. # 
  20. # [[2]]
  21. # [1] 3 5
  22. # attr(,"match.length")
  23. # [1] 1 1
  24. # attr(,"index.type")
  25. # [1] "chars"
  26. # attr(,"useBytes")
  27. # [1] TRUE
  28. # 
  29. # [[3]]
  30. # [1] 4 7
  31. # attr(,"match.length")
  32. # [1] 1 1
  33. # attr(,"index.type")
  34. # [1] "chars"
  35. # attr(,"useBytes")
  36. # [1] TRUE

substr {base} 系列

提取或者替换元素中起始位置之间的内容。

  1. x <- c("abc123","abc456","abc789")
  2. substr(x, start=2, stop=4)
  3. # [1] "bc1" "bc4" "bc7"
  5. substring(x, first=2) # stop = 1000000L
  6. # [1] "bc123" "bc456" "bc789"
  8. substr(x, start=2, stop=4) <- "***"
  9. x
  10. # [1] "a***23" "a***56" "a***89"

paste() 和 strsplit()

粘合和分割字符串

  1. paste("a","b",sep="-")
  2. # [1] "a-b"
  4. strsplit(c("a-b","c-d"),split="-")
  5. # [[1]]
  6. # [1] "a" "b"
  7. # 
  8. # [[2]]
  9. # [1] "c" "d"

学了这些发现提取特定模式里的字符串用基础函数还是很麻烦，还是去学习stringr包吧。