Update a Value in One Column Based on Criteria in Other Columns

Question

If my data frame (df) looks like this:

Name        State John Smith  MI John Smith  WI Jeff Smith  WI 

I want to rename the John Smith from WI "John Smith1". What is the cleanest R equivalent of the SQL statement?

update df  set Name = "John Smith1" where Name = "John Smith" and State = "WI" 

Answer 1

df <- data.frame(Name=c('John Smith', 'John Smith', 'Jeff Smith'),                  State=c('MI','WI','WI'), stringsAsFactors=F)  df <- within(df, Name[Name == 'John Smith' & State == 'WI'] <- 'John Smith1')  > df          Name State 1  John Smith    MI 2 John Smith1    WI 3  Jeff Smith    WI 

** Edit **

Edited to add that you can put whatever you like in the within expression:

df <- within(df, {     f <- Name == 'John Smith' & State == 'WI'     Name[f] <- 'John Smith1'     State[f] <- 'CA' })  

Answer 2

One way:

df[df$Name == "John_Smith" & df$State == "WI", "Name"] <- "John_Smith1" 

Another way using the dplyr:

df %>% mutate(Name = ifelse(State == "WI" & Name == "John_Smith", "John_Smith1", Name)) 

Note: As David Arenburg says, the first column should not be a factor. For this, reading the data set stringsAsFactors = FALSE.