LearningR-数据处理

另外还有一个paste0函数，默认就是sep=""

5.3 分割字符 strsplit

strsplit(x,split,fixed = FALSE,perl = FALSE,useBytes = FALSE)

x <- c(as = "asfef",qu = "qwerty","yuiop[","b","stuff.blah.yech")
strsplit(x,"e")
#需要注意的细节
strsplit(paste(c("","")
strsplit(""," ")[[1]]
strsplit(" "," ")[[1]]

##倒序运用：
strReverse <- function(x)
        sapply(lapply(strsplit(x,NULL),rev),paste,collapse = "")
strReverse(c("abc","Statistics"))

5.4 提取字符 substr与substring

substr(x,start,stop)
substring(text,first,last = 1000000L)
substr(x,stop) <- value
substring(text,last = 1000000L) <- value

substr("abcdef",4)
substring("abcdef",1:6,1:6)

substr(rep("abcdef",4),1:4,4:5)
x <- c("asfef","qwerty","stuff.blah.yech")
substr(x,5)
substring(x,4:6)
substring(x,2) <- c("..","+++")

5.5 替换字符 sub和gsub

• sub 只做一次替换（不管有几次匹配）

• gsub 把满足条件的匹配都做替换

sub(pattern,replacement,x,ignore.case = FALSE,useBytes = FALSE)
gsub(pattern,useBytes = FALSE)

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