For loop error: replacement has length zero

Question

I'm trying to match values between two data frames based on one column, and then assign a corresponding value to one of the data frames. Here is what the data look like

head(test1)
    zip dat.citystate
1   80914              
2   32920              
3   80914              
4   80914              
5   80914              
6   80914                

head(test2)
    zip          citystate
1 35004          Moody, AL
2 35005     Adamsville, AL
3 35006          Adger, AL
4 35007      Alabaster, AL
5 35010 Alexander City, AL
6 35011 Alexander City, AL

The dat.citystate column in test1 is an empty string "" .

I want to loop through test1 and find the city-state value from test2 that shares the same zip code, and add that to the corresponding row for test1 . Here is my for loop:

for (i in  1:nrow(test1)){
  test1$dat.citystate[i] <- test2$citystate[test2$zip == test1$zip[i]])
}

However, I get the following error code:

Error: replacement has length zero

I've looked everywhere but can't figure out what this means or where the error is coming from. Any suggestions?

Answer 1

Base R solution (in your sample data you currently have no matches):

test1$dat.citystate <- with(test2, citystate[match(test1$zip, zip)])

Data:

test1 <- structure(list(zip = c(80914L, 32920L, 80914L, 80914L, 80914L, 
80914L), dat.citystate = c("Moody, AL", NA, "Moody, AL", "Moody, AL", 
"Moody, AL", "Moody, AL")), row.names = c(NA, -6L), class = "data.frame")

test2 <- structure(list(`zip citystate` = c("80914 Moody, AL", "35005 Adamsville, AL", 
"35006 Adger, AL", "35007 Alabaster, AL", "35010 Alexander City, AL", 
"35011 Alexander City, AL"), zip = c(80914, 35005, 35006, 35007, 
35010, 35011), citystate = c("Moody, AL", "Adamsville, AL", "Adger, AL", 
"Alabaster, AL", "Alexander City, AL", "Alexander City, AL")), row.names = c(NA, 
-6L), class = "data.frame")