Perform large no. of iterations efficiently without using for loops

Question

I have a vector containing numeric elements like below:

jnk1<-c(0,2,1,3,4,2,1,2)

In another character vector I want to assign colors corresponding to each element of numeric vector jnk1.

m<-c("red","green","blue","brown","purple","green","blue","green")

I've written the following code using for loops to automate the process:

m<-as.character()
for (i in 1:length(jnk1)){
for (j in 1:length(jnk1)){
for (k in 1:length(jnk1)){
for (l in 1:length(jnk1)){
for (o in 1:length(jnk1)){
if (jnk1[i]==0){
m[i]<-c("red")}
if (jnk1[j]==1){
m[j]<-c("blue")}
if (jnk1[k]==2){
m[k]<-c("green")}
if (jnk1[l]==3){
m[l]<-c("brown")}
if (jnk1[o]==4){
m[o]<-c("purple")}}}}}}

The above code gets the job done for small number of iterations but for larger iterations it is quite inefficient and time consuming. Is it possible to get the job done using a more efficient code?

Use `match` maybe? Could you add what you expect as your result? — NelsonGon, Jan 02 '20 at 14:43
The expected result is the character contents of the character vector m — Debjyoti, Jan 02 '20 at 14:47
Do you have the pairing stored somewhere ? 0 -> red 1 - > blue etc ? This might be helpful - https://stackoverflow.com/questions/7547597/dictionary-style-replace-multiple-items/ — Ronak Shah, Jan 02 '20 at 14:48
That was a mistake, I've edited it, thanks for pointing it out — Debjyoti, Jan 02 '20 at 15:14
Are you only trying to create a vector? or is a data.frame acceptable? — akash87, Jan 02 '20 at 15:19

score 5 · Answer 1 · answered Jan 02 '20 at 14:51

A pretty straightforward way to do this would be to use a lookup vector (note that the +1 is necessary since R indices start at 1 and the minimum value in your vector is 0).

lookup <- c('red', 'blue', 'green', 'brown', 'pink')
m <- lookup[jnk1+1]

It's also worth noting that you could use a single for loop, you don't need a separate index in each if condition.

Perform large no. of iterations efficiently without using for loops

1 Answers1