CODEWITHSUNDEEP
rdataframenested-loops
Michal
Michal

Reputation: 1905

Add a column to a data frame based on values of another data frame

I have a data frame with temperatures from summer 2013. I would like to map the temperatures geographically using their latitude and longitude based on this example. I have a dataset with the temperatures and zip codes and I would like to add a column with the appropriate lat and long to my original data frame.

I wrote a nested loop that works but is terribly inefficient:

for (i in 1:length(Summer2013$zipcode)) {
  for (j in 1:length(zipcode$zip)) {
    col[i] <- if (Summer2013$zipcode[i] == zipcode$zip[j]) {
      zipcode$longitude[j] 
    } else {0}
  }
}

(so far I thought I'd just try doing the long and when I figured out something better, I was going to do the lat as well)

I know that R is able to perform loops using column assignments but I was afraid of not getting an expected result so wanted to err on the side of caution.

Upvotes: 2

Views: 270

Answers (1)

rrs
rrs

Reputation: 9903

you want to merge the datasets:

merge(Summer2013, zipcode, by.x="zipcode", by.y="zip", all.x=TRUE)

this is a left join and will return NA for zipcodes it can't find in the zipcode data frame.

Upvotes: 1

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