R中字段抽取、字段合并、字段匹配

1、字段抽取

字段抽取，是根据已知列数据的开始和结束位置，抽取出新的列

字段截取函数：substr(x,start,stop)

tel <- '18922254812';#运营商band <- substr(tel, 1, 3)#地区area <- substr(tel, 4, 7)#号码段num <- substr(tel, 8, 11)tels <- read.csv('1.csv');#运营商bands <- substr(tels[,1], 1, 3)#地区areas <- substr(tels[,1], 4, 7)#号码段nums <- substr(tels[,1], 8, 11)new_tels <- data.frame(tels, bands, areas, nums)

2、字段合并

字段合并，是指将同一个数据框中的不同列，进行合并，形成新的列

字符分割函数：paste(x1,x2,...,sep=" ")

data <- read.table('1.csv', sep=' ')p_data <- paste(data[,1], data[,2], data[,3], sep="")newData <- data.frame(data, p_data)

3、记录合并

将两个结构相同的数据框，合并成一个数据框

记录合并函数：rbind(dataFrame1,dataFrame2,...)

data_1_1 <- read.table('1.csv', sep='|', header=TRUE, fileEncoding='utf-8');data_1_2 <- read.table('2.csv', sep='|', header=TRUE, fileEncoding='utf-8');data_1_3 <- read.table('3.csv', sep='|', header=TRUE, fileEncoding='utf-8');data <- rbind(data_1_1, data_1_2, data_1_3)fix(data)

4、字段匹配

将不同结构的数据框，按照一定的条件进行合并（两表合并）

字段匹配函数：merge(x,y,by.x,by.y)

items <- read.table('1.csv', sep='|', header=FALSE, fileEncoding='utf-8')fix(items)prices <- read.table('2.csv', sep='|', header=FALSE, fileEncoding='utf-8')fix(prices)itemPrices <- merge(prices, items, by.x=c('V1'), by.y=c('V1'))fix(itemPrices)

Join( )也可以用来实现两表连接：

inner_join(t1,t2,by=c("列名1","列名2"))#功能等于：merge(t1,t2,by.x="列名",by.y="列名")#还有其他的join方式：full_join 全连接left_join 左连接right_join 右连接

5、字符串处理高级技巧

x <- c("Hellow", "World", "!") #一、字符串长度nchar(x)#[1] 6 5 1length(x)#[1] 3#二、字符串替换chartr("HW", "ZX", x)#[1] "Zellow" "Xorld"  "!"     #三、字符串的大小写转换tolower(x)#[1] "hellow" "world"  "!"toupper(x)#[1] "HELLOW" "WORLD"  "!"     #四、字符串的拼接paste("CK", 1:6, sep="")#[1] "CK1" "CK2" "CK3" "CK4" "CK5" "CK6" x <- list(a="aaa", b="bbb", c="ccc") y <- list(d=1, e=2) paste(x, y, sep="-")     #较短的向量被循环使用 #[1] "aaa-1" "bbb-2" "ccc-1" #五、字符串切割text <- "Hello word!"strsplit(text, ' ')#[[1]]#[1] "Hello" "word!"class(strsplit(text, ' '))#[1] "list"#有一种情况很特殊：#如果split参数的字符长度为0，得到的结果就是一个个的字符：strsplit(text, '')#[[1]]# [1] "H" "e" "l" "l" "o" " " "w" "o" "r" "d" "!"#一个首字符大写的综合案例capStringAll <- function(x)  {  s <- strsplit(x, " ")[[1]]  paste(toupper(substring(s, 1, 1)), substring(s, 2),        sep = "", collapse = " ")}capStringAll("hello word")#[1] "Hello Word"capString <- function(x)   {  s <- strsplit(x, " ")[[1]]  s[1] <- paste(toupper(substring(s[1], 1, 1)), substring(s[1], 2), sep = "", collapse = " ");  paste(s, sep = "", collapse = " ")}capString("hello word")#[1] "Hello word"#六、字符串的查找#grep, grepl: 返回pattern的匹配项。#前者返回匹配项目的下标；后者返回逻辑值，x长度有多少，就返回多少个逻辑值。#如果添加一个value参数，赋值为T，则返回匹配项的值。text <- c("Company", "Coworker", "Cooperation", "Can")grep("o", text)#[1] 1 2 3grepl("o", text)#[1]  TRUE  TRUE  TRUE FALSEgrep("o", text, value = T)#[1] "Company"     "Coworker"    "Cooperation"#七、字符串的替换#sub, gsub: 返回用replacement替换匹配项之后的x(字符型向量)。#前者只替换向量中每个元素的第一个匹配值，后者替换所有匹配值。#注意以下两个例子中"o"的替换方式。sub("o", "xx", text)#[1] "Cxxmpany"     "Cxxworker"    "Cxxoperation" "Can" gsub("o", "xx", text)#[1] "Cxxmpany"     "Cxxwxxrker"   "Cxxxxperatixxn" "Can"#八、字符串的截取x <- "123456789" substr(x, 2, 4) #[1] "234" substring(x, c(2,4), c(4,5,8)) #[1] "234"     "45"      "2345678"