R ifelse with match

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I have a dataframe 'df' that looks like this:

LatName ComName
Todd Smith Becky Jones
Becky Jones
Becky Jones
Rachel Adams

And another dataframe 'df2' that looks like this:

LatinName CommonName
Brad Robbins Becky Jones
Steve Reisen Rachel Adams
Connor McDougal Charlie Williams

If want to match values in ComName and CommonName and if they match fill in LatName with LatinName only if LatName is empty to begin with. If LatName isn't empty, then I want that entry left alone, so that the end result of df looks like this:

LatName ComName
Todd Smith Becky Jones
Brad Robbins Becky Jones
Brad Robbins Becky Jones
Steve Reisen Rachel Adams

I left the blank row in there on purpose because some of my rows have nothing in them.

Thank you!

match conditional-statements if-statement r
1 Answers

We could do a join and then coalesce

library(dplyr)
left_join(df1, df2, by = c("ComName" = "CommonName")) %>%
   mutate(LatName = coalesce(na_if(LatName, ""), LatinName)

-output

    LatName      ComName
1   Todd Smith  Becky Jones
2 Brad Robbins  Becky Jones
3 Brad Robbins  Becky Jones
4 Steve Reisen Rachel Adams

data

df1 <- structure(list(LatName = c("Todd Smith", NA, NA, NA),
 ComName = c("Becky Jones", 
"Becky Jones", "Becky Jones", "Rachel Adams")), class = "data.frame", 
row.names = c(NA, 
-4L))

df2 <- structure(list(LatinName = c("Brad Robbins", "Steve Reisen", 
"Connor McDougal"), CommonName = c("Becky Jones", "Rachel Adams", 
"Charlie Williams")), class = "data.frame", row.names = c(NA, 
-3L))
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