how to create a list in R from two vectors (one would be the keys, the other the values)?

Question

I have two vectors and I want to create a list in R where one vector are the keys and the other the values. I thought that I was going to find easily the answer in my books

Answer 1

Another serious option here , is to use data.table. Which use the key to sort your structure and it is very fast to access elements specially when you have a large numbers . Here an example:

library(data.table)   
DT <- data.table(xx = 1:1e6, 
             k = paste0("key", 1:1e6),key="k")

Dt is a data.table with 2 columns , where I set the column k as a key. DT xx k 1: 1 key1 2: 10 key10 3: 100 key100 4: 1000 key1000 5: 10000 key10000 ---
999996: 999995 key999995 999997: 999996 key999996 999998: 999997 key999997 999999: 999998 key999998 1000000: 999999 key999999

Now I can access my data.table using the key like this:

DT['key1000']
         k   xx
1: key1000 1000

Here a benchmarking comparing the data.table solution to a named vector:

vals <- 1:1000000
DT <- data.table(xx = vals ,
                 k = paste0("key", vals),key="k")
keys <- paste0("key", vals)
names(vals) <- keys
library(microbenchmark)
microbenchmark( vals["key42"],DT["key42"],times=100)

Unit: microseconds
          expr        min          lq     median         uq        max neval
 vals["key42"] 111938.692 113207.4945 114924.010 130010.832 361077.210   100
   DT["key42"]    768.753    797.0085   1055.661   1067.987   2058.985   100