invalid factor level, NA generated

[nortiz]

Hello,

I'm trying to create a new variable 'value' in the data frame, and assign either the value of its corresponding 'src' or 'dst' if 'group' is either 'A' or 'B'. But I get 'NA' in 'B' instead of 'C1' ('dst') with a warning of ': invalid factor level, NA generated'

Could anyone help me to understand what the issue is with the factors here?
What am I doing wrong and what is the right way to do it?

Many thanks in advance,

library(tidyverse)
#> Warning: package 'ggplot2' was built under R version 3.6.2

dF <- data.frame(
  group = c("A","A","B"),
  src = c("O1","O2", "O3"),
  dst = c("C1","C2","C1")
)

dF <- dF %>%
  mutate(
    value = group == "A",
    value = if_else(value == TRUE, src, dst)
  )
#> Warning in `[<-.factor`(`*tmp*`, i, value = structure(1L, .Label =
#> c("C1", : invalid factor level, NA generated

dF
#>   group src dst value
#> 1     A  O1  C1    O1
#> 2     A  O2  C2    O2
#> 3     B  O3  C1  <NA>

^{Created on 2021-07-14 by the reprex package (v2.0.0)}

[HanOostdijk]

This is related to the conversion of strings to factors in your data.frame.
And I think this is dependent on your version of R.
See the two cases in the next reprex. My default for stringsAsFactors seems to be FALSE .

library(dplyr)
#> 
#> Attaching package: 'dplyr'
#> The following objects are masked from 'package:stats':
#> 
#>     filter, lag
#> The following objects are masked from 'package:base':
#> 
#>     intersect, setdiff, setequal, union

dF1 <- data.frame(
  group = c("A","A","B"),
  src = c("O1","O2", "O3"),
  dst = c("C1","C2","C1"),
  stringsAsFactors = T
)

dF1 <- dF1 %>%
  mutate(
    value = group == "A",
    value = if_else(value == TRUE, src, dst)
  )
#> Warning in `[<-.factor`(`*tmp*`, i, value = structure(1L, .Label = c("C1", :
#> invalid factor level, NA generated

dF1
#>   group src dst value
#> 1     A  O1  C1    O1
#> 2     A  O2  C2    O2
#> 3     B  O3  C1  <NA>

dF2 <- data.frame(
  group = c("A","A","B"),
  src = c("O1","O2", "O3"),
  dst = c("C1","C2","C1"),
  stringsAsFactors = F
)

dF2 <- dF2 %>%
  mutate(
    value = group == "A",
    value = if_else(value == TRUE, src, dst)
  )

dF2
#>   group src dst value
#> 1     A  O1  C1    O1
#> 2     A  O2  C2    O2
#> 3     B  O3  C1    C1
Created on 2021-07-15 by the reprex package (v2.0.0)

 Session info
sessioninfo::session_info()
#> - Session info ---------------------------------------------------------------
#>  setting  value                       
#>  version  R version 4.1.0 (2021-05-18)
#>  os       Windows 10 x64              
#>  system   x86_64, mingw32             
#>  ui       RTerm                       
#>  language (EN)                        
#>  collate  English_United States.1252  
#>  ctype    English_United States.1252  
#>  tz       Europe/Berlin               
#>  date     2021-07-15                  
#> 
#> - Packages -------------------------------------------------------------------
#>  package     * version date       lib source        
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#>  backports     1.1.6   2020-04-05 [1] CRAN (R 4.0.0)
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#> 
#> [1] D:/tools/R/Packages
#> [2] D:/tools/R/R-4.1.0/library

[nortiz]

Many thanks @HanOostdijk for your help. You're right, my issue was easy solved by just changing the factors to strings.

Have a great day!