Question

I am working on map data structure in which i need to store key value pair.

 map[key1]<-value1
 map[key2]<-value2
 map[key3]<-value3
 map[key4]<-value4

I need to get value based on key. How can i implement this in R?

Answer 1

Use a list, because a simple vector constructed with c can’t handle anything more than scalar values:

> map = c(key1 = c(1,2,3), key2 = 2, key3 = 3)
> map[["key1"]]
Error in map[["key1"]] : subscript out of bounds

why does this fail? because map is now:

> map
key11 key12 key13  key2  key3 
    1     2     3     2     3 

use a list instead:

> map = list(key1 = c(1,2,3), key2 = 2, key3 = 3)
> map[["key1"]]
[1] 1 2 3

also dynamically extensible:

> map[["key99"]]="Hello You!"
> map
$key1
[1] 1 2 3

$key2
[1] 2

$key3
[1] 3

$key99
[1] "Hello You!"

Start with an empty map=list() if you are building one up.