找出给定数字在R中的向量序列中的位置

Question

I have three variables a1, a2 and a3.

a1 <- 1:10
a2 <- 11:20
a3 <- 21:30

then I have another variable called my.numbers <- c(1, 20, 22,11)

I want to find out where these numbers are located. So the result I want is:

1 in a1
20 in a2
22 in a3
11 in a2

Any suggestion on how it can be done easy way?

Answer 1

For the record here is how you can get out the exact result in the question.

a1 <- 1:10
a2 <- 11:20
a3 <- 21:30

L<-list("a1"=a1,"a2"=a2,"a3"=a3)
my.numbers <- c(1, 20, 22, 11)

func<-function(item){
    my.numbers[which(my.numbers %in% item)]
}

Fin<-lapply(L, func)

for(i in 1:length(Fin)){
Index<-unlist(Fin[i])
name<-paste("a",i, sep="")
    for(i in 1:length(Index)){
       print(paste(Index[i], "in", name))
    }
}

[1] "1 in a1"
[1] "20 in a2"
[1] "11 in a2"
[1] "22 in a3"

Answer 2

With a couple purrr::map functions, you can work across the numbers, then within that, across the a vectors.

I'm making a list of the a vectors with tibble::lst because it sets the names of the list as the names of the variables going into it—convenient for something like this where it's the name of the list item that's important.

library(tidyverse)

a_list <- lst(a1, a2, a3)

my.numbers %>%
  map_chr(function(num) {
    which_a <- map_lgl(a_list, ~(num %in% .))
    a_name <- names(a_list)[which_a]
    str_glue("{num} in {a_name}")
  })
#> [1] "1 in a1"  "20 in a2" "22 in a3" "11 in a2"

You could use match or another function after the map_lgl instead—I left it verbose to make it a little more clear what's going on.