nchar

取字元數量的函式
length與nchar不同，length是取向量的長度

# nchar表示字串中的字元的個數
nchar("abcd")
[1] 4

# length表示向量中元素的個數
length("abcd")
[1] 1
length(c("hello", "world"))
[1] 2

chartr

字元替換

chartr(old="a", new="c", x="a123")
[1] "c123"

chartr(old="a", new="A", x="data")
[1] "dAtA"

paste和paste0

字串粘合函式
paste在不指定分割符的情況下，預設分割符是空格

# 預設以空格隔開
paste("Hello","world")
[1] "Hello world"

# 沒有空格
paste0("Hello","world")
[1] "Helloworld"

# 指定分割符
paste("abc", "efg", "hijk", sep = "-")
[1] "abc-efg-hijk"

# 分別對向量的每一個元素進行連線
paste0("A", 1:6, sep = "")
[1] "A1" "A2" "A3" "A4" "A5" "A6"

# collapse引數：每一個元素操作之後，再把向量的每一個元素進行連線
 

paste0("A", 1:6, sep = "",collapse = "-")
[1] "A1-A2-A3-A4-A5-A6"

substr

字串擷取函式

substr(x = "hello", start = 1, stop = 2)
[1] "he"

strsplit

字串的分割函式，可以指定分割符，生成一個list

strsplit("abc", split = "")
[[1]]
[1] "a" "b" "c"

如果要對一個向量使用該函式，需要注意。

# 分割向量的每一個元素，並取分割後的第一個元素
unlist(lapply(X = c("abc"
 
, "bcd", "dfafadf"), FUN = function(x) {return(strsplit(x, split = "")[[1]][1])}))
[1] "a" "b" "d"

gsub和sub

字串替換
gsub替換匹配到的全部
sub 替換匹配到的第一個

# 將b替換為B
gsub(pattern = "b", replacement = "B", x = "baby")
[1] "BaBy"

gsub(pattern = "b", replacement = "B", x = c("abcb", "boy", "baby"))
[1] "aBcB" "Boy"  "BaBy"

# 只替換第一個b
sub(pattern = "b", replacement = "B", x = "baby")
[1] "Baby"

sub(pattern = "b", replacement = "B", x = c("abcb", "baby"))
[1] "aBcb" "Baby"

grep和grepl

字串匹配
grep函式返回的是索引值
grepl函式返回的是邏輯值

# 返回匹配到的元素的索引
grep(pattern = "boy", x = c("abcb", "boy", "baby"))
[1] 2

# 返回邏輯值
grepl(pattern = "boy", x = c("abcb", "boy", "baby"))
[1] FALSE  TRUE FALSE

match && pmatch &&charmatch

1、match
Usage
match(x, table, nomatch = NA_integer_, incomparables = NULL)
x %in% table

引數：
x: vector or NULL: the values to be matched. Long vectors are supported.

table : vector or NULL: the values to be matched against. Long vectors are not supported. (被匹配的值)

nomatch: the value to be returned in the case when no match is found. Note that it is coerced to integer. (沒有match上的返回的值)

incomparables : a vector of values that cannot be matched. Any value in x matching a value in this vector is assigned the nomatch value. For historical reasons, FALSE is equivalent to NULL. (不同來匹配的值)

match函式類似與 %in%，不同的是match返回的是索引，而%in%返回的是邏輯值。