nchar

取字符数量的函数

length与nchar不同，length是取向量的长度

# nchar表示字符串中的字符的个数nchar("abcd")[1] 4# length表示向量中元素的个数length("abcd")[1] 1length(c("hello", "world"))[1] 2

chartr

字符替换

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

paste和paste0

字符串粘合函数

paste在不指定切割符的情况下，默认切割符是空格

paste0在不指定切割符的情况下，默认切割符是空

# 默认以空格隔开paste("Hello","world")[1] "Hello world"# 没有空格paste0("Hello","world")[1] "Helloworld"# 指定切割符paste("abc", "efg", "hijk", sep = "-")[1] "abc-efg-hijk"# 分别对向量的每个元素进行连接paste0("A", 1:6, sep = "")[1] "A1" "A2" "A3" "A4" "A5" "A6"# collapse參数：每个元素操作之后，再把向量的每个元素进行连接paste0("A", 1:6, sep = "",collapse = "-")[1] "A1-A2-A3-A4-A5-A6"

substr

字符串截取函数

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

strsplit

字符串的切割函数，能够指定切割符。生成一个list

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

假设要对一个向量使用该函数。须要注意。

# 切割向量的每个元素，并取切割后的第一个元素unlist(lapply(X = c("abc", "bcd", "dfafadf"), FUN = function(x) {
     return(strsplit(x, split = "")[[1]][1])}))[1] "a" "b" "d"

gsub和sub

字符串替换

gsub替换匹配到的所有

sub 替换匹配到的第一个

# 将b替换为Bgsub(pattern = "b", replacement = "B", x = "baby")[1] "BaBy"gsub(pattern = "b", replacement = "B", x = c("abcb", "boy", "baby"))[1] "aBcB" "Boy"  "BaBy"# 仅仅替换第一个bsub(pattern = "b", replacement = "B", x = "baby")[1] "Baby"sub(pattern = "b", replacement = "B", x = c("abcb", "baby"))[1] "aBcb" "Baby"

grep和grepl

字符串匹配

grep函数返回的是索引值

grepl函数返回的是逻辑值

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

參数：

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. (没有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. (不同来匹配的值)

match函数相似与 %in%，不同的是match返回的是索引，而%in%返回的是逻辑值。