R function to paste information from different columns?

I have a data frame with 3 different identifications and sometimes they overlap. I want to create a new column, with only one of those ids, in an order of preference (id1>id2>id3). Ex.:

id1  id2   id3
12   145   8763
45   836   5766
13   768   9374
     836   5766
12   145   
           9282
     567   
45   836   5766

and I want to have:

    id1  id2   id3    id.new
    12   145   8763   12
    45   836   5766   45
    13   768   9374   13
         836   5766   836
               9282   9282
         567          567

I have tried the if else,which, grep functions.. but I can't make it work.

Ex. of my try:

df$id1 <- ifelse(df$id1 == "", paste(df$2), (ifelse(df$id1)))

I am able to do this on Excel, but I am switching to R, for being more reliable and reproducible :) But in excel I would use:

=if(A1="",B1,(if(B1="",C1,B1)),A1)

Solution

Using coalesce from the dplyr package, we can try:

library(dplyr)
df$id.new <- coalesce(df$id1, df$id2, df$id3)
df

  id1 id2  id3 id.new
1  12 145 8763     12
2  45 836 5766     45
3  13 768 9374     13
4  NA 836 5766    836
5  12 145   NA     12
6  NA  NA 9282   9282
7  NA 567   NA    567
8  45 836 5766     45

Data:

df <- data.frame(id1=c(12,45,13,NA,12,NA,NA,45),
                 id2=c(145,836,768,836,145,NA,567,836),
                 id3=c(8763,5766,9374,5766,NA,9282,NA,5766))