strsplit函数
ids
a<-strsplit(as.character(ids[,2]), " /// ")#a就变成列表，ids有多少行，就生成多少列表
a
mapply函数
tmp <- mapply( cbind, ids[,1], a ) #将ids和a按列合并
tmp
strsplit函数
> x = c("abcde", "ghij", "klmnopq")
> strsplit(x, "", fixed=TRUE)
[[1]]
[1] "a" "b" "c" "d" "e"
[[2]]
[1] "g" "h" "i" "j"
[[3]]
[1] "k" "l" "m" "n" "o" "p" "q"
mapply函数
> mapply(sum, list(a=1,b=2,c=3), list(a=10,b=20,d=30))
a b c
11 22 33
> mapply(function(x,y) x^y, c(1:5), c(1:5))
[1] 1 4 27 256 3125
> mapply(function(x,y) c(x+y, x^y), c(1:5), c(1:5))
[,1] [,2] [,3] [,4] [,5]
[1,] 2 4 6 8 10
[2,] 1 4 27 256 3125
paste函数
> paste(1:12, c("st", "nd", "rd", rep("th", 9)),sep = "",collapse = ",")
[1] "1st,2nd,3rd,4th,5th,6th,7th,8th,9th,10th,11th,12th"
> paste(1:12, c("st", "nd", "rd", rep("th", 9)))
[1] "1 st" "2 nd" "3 rd" "4 th" "5 th" "6 th" "7 th"
[8] "8 th" "9 th" "10 th" "11 th" "12 th"
> paste0(1:12)
[1] "1" "2" "3" "4" "5" "6" "7" "8" "9" "10" "11"
[12] "12"
> ## When passing a single vector, paste0 and paste work like as.character.
> paste0(1:12)
[1] "1" "2" "3" "4" "5" "6" "7" "8" "9" "10" "11" "12"
> paste(1:12) # same
[1] "1" "2" "3" "4" "5" "6" "7" "8" "9" "10" "11" "12"
> as.character(1:12) # same
[1] "1" "2" "3" "4" "5" "6" "7" "8" "9" "10" "11" "12"
> ## If you pass several vectors to paste0, they are concatenated in a
> ## vectorized way.
> (nth <- paste0(1:12, c("st", "nd", "rd", rep("th", 9))))
[1] "1st" "2nd" "3rd" "4th" "5th" "6th" "7th" "8th" "9th" "10th" "11th" "12th"
> ## paste works the same, but separates each input with a space.
> ## Notice that the recycling rules make every input as long as the longest input.
> paste(month.abb, "is the", nth, "month of the year.")
[1] "Jan is the 1st month of the year." "Feb is the 2nd month of the year."
[3] "Mar is the 3rd month of the year." "Apr is the 4th month of the year."
[5] "May is the 5th month of the year." "Jun is the 6th month of the year."
[7] "Jul is the 7th month of the year." "Aug is the 8th month of the year."
[9] "Sep is the 9th month of the year." "Oct is the 10th month of the year."
[11] "Nov is the 11th month of the year." "Dec is the 12th month of the year."
> paste(month.abb, letters)
[1] "Jan a" "Feb b" "Mar c" "Apr d" "May e" "Jun f" "Jul g" "Aug h" "Sep i" "Oct j"
[11] "Nov k" "Dec l" "Jan m" "Feb n" "Mar o" "Apr p" "May q" "Jun r" "Jul s" "Aug t"
[21] "Sep u" "Oct v" "Nov w" "Dec x" "Jan y" "Feb z"
> ## You can change the separator by passing a sep argument
> ## which can be multiple characters.
> paste(month.abb, "is the", nth, "month of the year.", sep = "_*_")
[1] "Jan_*_is the_*_1st_*_month of the year." "Feb_*_is the_*_2nd_*_month of the year."
[3] "Mar_*_is the_*_3rd_*_month of the year." "Apr_*_is the_*_4th_*_month of the year."
[5] "May_*_is the_*_5th_*_month of the year." "Jun_*_is the_*_6th_*_month of the year."
[7] "Jul_*_is the_*_7th_*_month of the year." "Aug_*_is the_*_8th_*_month of the year."
[9] "Sep_*_is the_*_9th_*_month of the year." "Oct_*_is the_*_10th_*_month of the year."
[11] "Nov_*_is the_*_11th_*_month of the year." "Dec_*_is the_*_12th_*_month of the year."
> ## To collapse the output into a single string, pass a collapse argument.
> paste0(nth, collapse = ", ")
[1] "1st, 2nd, 3rd, 4th, 5th, 6th, 7th, 8th, 9th, 10th, 11th, 12th"
> ## For inputs of length 1, use the sep argument rather than collapse
> paste("1st", "2nd", "3rd", collapse = ", ") # probably not what you wanted
[1] "1st 2nd 3rd"
> paste("1st", "2nd", "3rd", sep = ", ")
[1] "1st, 2nd, 3rd"
> ## You can combine the sep and collapse arguments together.
> paste(month.abb, nth, sep = ": ", collapse = "; ")
[1] "Jan: 1st; Feb: 2nd; Mar: 3rd; Apr: 4th; May: 5th; Jun: 6th; Jul: 7th; Aug: 8th; Sep: 9th; Oct: 10th; Nov: 11th; Dec: 12th"
match函数
user_id<-c('A','B','C','D')
u1<-c('B','C','D','A')
e1<-c('a1','a2','a3','a4')
m1<-data.frame(u1,e1)
t1<-match(user_id,m1$u1)
t1
[1] 4 1 2 3
x<-m1[match(user_id,m1$u1),]
x
u1 e1
4 A a4
1 B a1
2 C a2
3 D a3
第一个t1得到的是user_id在m1$u1里面的坐标位置，也就是说接下来只能是从m1里取子集，取出来的子集的顺序是按user_id的顺序来的。