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rif-statementdplyrcase-when

Case When LIKE equivalent in R

I am wanting to do similar to a case statement in r for a variable utilizing an ifelse statement. For example, lets say I have the following column vector 'Letter_Test' in a data frame that has:

Alpha - Test, Beta- Test, Zeta-Test, Alpha-Two, Beta-Two

I'd like to write a statement that says basically if data is like Alpha then 'Alpha', else return the column result.

In SQL that would be (CASE WHEN Letter_Test LIKE '%Alpha%' THEN Alpha else 'Letter-Test' end).

Solution

  • Actually not sure if I got the question right but if you mean you want to test if "Alpha" is in the column Letter-Test, then this works:

        > df <- data.frame("Letter-Test" = c("Alpha - Test", "Beta- Test", "Zeta-Test", "Alpha-Two", "Beta-Two"),
+                  stringsAsFactors = FALSE)
> 
> ifelse(test = grepl("Alpha", df$Letter.Test), yes = "Alpha", no = df$Letter.Test)
[1] "Alpha"      "Beta- Test" "Zeta-Test"  "Alpha"      "Beta-Two"

    Test takes TRUE and FALSE, grepl returns TRUE if the word was found inside the column Letter.Test.

    Or you can put the results directly into a new column in the data frame:

    > df$AplhaTest <- ifelse(test = grepl("Alpha", df$Letter.Test), yes = "Alpha", no = df$Letter.Test)
> df
   Letter.Test  AplhaTest
1 Alpha - Test      Alpha
2   Beta- Test Beta- Test
3    Zeta-Test  Zeta-Test
4    Alpha-Two      Alpha
5     Beta-Two   Beta-Two