如何将string拆分成给定长度的子string？
我有一个string，如：
"aabbccccdd"
我想把这个string分解成长度为2的子string的向量：
"aa" "bb" "cc" "cc" "dd"
这是一种方法
substring("aabbccccdd", seq(1, 9, 2), seq(2, 10, 2)) #[1] "aa" "bb" "cc" "cc" "dd"
或更一般地说
text <- "aabbccccdd" substring(text, seq(1, nchar(text)-1, 2), seq(2, nchar(text), 2)) #[1] "aa" "bb" "cc" "cc" "dd"
编辑：这很快，更快
sst <- strsplit(text, "")[[1]] out <- paste0(sst[c(TRUE, FALSE)], sst[c(FALSE, TRUE)])
它首先将string分解成字符。 然后，将偶数元素和奇怪元素粘贴在一起。
计时
text <- paste(rep(paste0(letters, letters), 1000), collapse="") g1 <- function(text) { substring(text, seq(1, nchar(text)-1, 2), seq(2, nchar(text), 2)) } g2 <- function(text) { sst <- strsplit(text, "")[[1]] paste0(sst[c(TRUE, FALSE)], sst[c(FALSE, TRUE)]) } identical(g1(text), g2(text)) #[1] TRUE library(rbenchmark) benchmark(g1=g1(text), g2=g2(text)) # test replications elapsed relative user.self sys.self user.child sys.child #1 g1 100 95.451 79.87531 95.438 0 0 0 #2 g2 100 1.195 1.00000 1.196 0 0 0
string <- "aabbccccdd" # total length of string num.chars <- nchar(string) # the indices where each substr will start starts <- seq(1,num.chars, by=2) # chop it up sapply(starts, function(ii) { substr(string, ii, ii+1) })
这使
[1] "aa" "bb" "cc" "cc" "dd"
有两个简单的可能性：
s <- "aabbccccdd"
-
gregexpr和regmatches：regmatches(s, gregexpr(".{2}", s))[[1]] # [1] "aa" "bb" "cc" "cc" "dd" -
strsplit：strsplit(s, "(?<=.{2})", perl = TRUE)[[1]] # [1] "aa" "bb" "cc" "cc" "dd"
可以使用matrix来分组字符：
s2 <- function(x) { m <- matrix(strsplit(x, '')[[1]], nrow=2) apply(m, 2, paste, collapse='') } s2('aabbccddeeff') ## [1] "aa" "bb" "cc" "dd" "ee" "ff"
不幸的是，这打破了input奇数string的长度，给出了一个警告：
s2('abc') ## [1] "ab" "ca" ## Warning message: ## In matrix(strsplit(x, "")[[1]], nrow = 2) : ## data length [3] is not a sub-multiple or multiple of the number of rows [2]
更不幸的是，来自@GSee的g1和g2默默地为奇数string长度的input返回不正确的结果：
g1('abc') ## [1] "ab" g2('abc') ## [1] "ab" "cb"
这是s2精神中的函数，对每个组中的字符数取一个参数，并在必要时留下最后一个条目：
s <- function(x, n) { sst <- strsplit(x, '')[[1]] m <- matrix('', nrow=n, ncol=(length(sst)+n-1)%/%n) m[seq_along(sst)] <- sst apply(m, 2, paste, collapse='') } s('hello world', 2) ## [1] "he" "ll" "o " "wo" "rl" "d" s('hello world', 3) ## [1] "hel" "lo " "wor" "ld"
（它确实比g2慢，但比g1快7倍）
丑陋但有用
sequenceString <- "ATGAATAAAG" J=3#maximum sequence length in file sequenceSmallVecStart <- substring(sequenceString, seq(1, nchar(sequenceString)-J+1, J), seq(J,nchar(sequenceString), J)) sequenceSmallVecEnd <- substring(sequenceString, max(seq(J, nchar(sequenceString), J))+1) sequenceSmallVec <- c(sequenceSmallVecStart,sequenceSmallVecEnd) cat(sequenceSmallVec,sep = "\n")
给予ATG AAT AAA G
