`paste`,`str_c`,`str_join`,`stri_join`,`stri_c`,`stri_paste`之间的区别？

Question

所有这些看似非常相似的功能之间有什么区别？

Answer 1

• stri_join,stri_c和stri_paste来自包装stringi,是纯粹的别名

• str_c来自stringr和只是stringi::stri_join一个参数ignore_null硬编码TRUE,而stringi::stri_join有它设置为FALSE默认.stringr::str_join是一个弃用的别名str_c

看到:

library(stringi)
identical(stri_join, stri_c)
# [1] TRUE
identical(stri_join, stri_paste)
# [1] TRUE

library(stringr)
str_c
# function (..., sep = "", collapse = NULL) 
# {
#   stri_c(..., sep = sep, collapse = collapse, ignore_null = TRUE)
# }
# <environment: namespace:stringr>

stri_joinbase::paste与下面列举的一些差异非常相似:

1. sep = ""默认情况下

所以它paste0在默认情况下表现得更像,但却paste0失去了它的sep论点.

identical(paste0("a","b")        , stri_join("a","b"))
# [1] TRUE
identical(paste("a","b")         , stri_join("a","b",sep=" "))
# [1] TRUE
identical(paste("a","b", sep="-"), stri_join("a","b", sep="-"))
# [1] TRUE

str_c会表现得像stri_join这里一样.

2.行为 NA

如果你粘贴到NA使用stri_join,结果是NA,paste转换NA为"NA"

paste0(c("a","b"),c("c",NA))
# [1] "ac"  "bNA"
stri_join(c("a","b"),c("c",NA))
# [1] "ac" NA

str_c也会像stri_join这里一样表现

3.具有长度0参数的行为

当遇到长度为0的值时,character(0)返回,除非ignore_null设置为FALSE,否则忽略该值.它不同于paste将长度0值转换为""并因此在输出中包含2个连续分隔符的行为.

stri_join("a",NULL, "b")  
# [1] character(0)
stri_join("a",character(0), "b")  
# [1] character(0)

paste0("a",NULL, "b")
# [1] "ab"
stri_join("a",NULL, "b", ignore_null = TRUE)
# [1] "ab"
str_c("a",NULL, "b")
# [1] "ab"

paste("a",NULL, "b") # produces double space!
# [1] "a  b" 
stri_join("a",NULL, "b", ignore_null = TRUE, sep = " ")
# [1] "a b"
str_c("a",NULL, "b", sep = " ")
# [1] "a b"

4. stri_join提醒更多

paste(c("a","b"),c("c","d","e"))
# [1] "a c" "b d" "a e"
paste("a","b", sep = c(" ","-"))
# [1] "a b"

stri_join(c("a","b"),c("c","d","e"), sep = " ")
# [1] "a c" "b d" "a e"
# Warning message:
#   In stri_join(c("a", "b"), c("c", "d", "e"), sep = " ") :
#   longer object length is not a multiple of shorter object length
stri_join("a","b", sep = c(" ","-"))
# [1] "a b"
# Warning message:
#   In stri_join("a", "b", sep = c(" ", "-")) :
#   argument `sep` should be one character string; taking the first one

5. stri_join更快

microbenchmark::microbenchmark(
  stringi = stri_join(rep("a",1000000),rep("b",1000),"c",sep=" "),
  base    = paste(rep("a",1000000),rep("b",1000),"c")
)

# Unit: milliseconds
#    expr       min       lq      mean    median       uq      max neval cld
# stringi  88.54199  93.4477  97.31161  95.17157  96.8879 131.9737   100  a 
# base    166.01024 169.7189 178.31065 171.30910 176.3055 215.5982   100   b