for loop through a list of data frames and save results in new data frame

Question

I want to fetch some values out of a list of data frames and save the results in a new data frame. This is how my code looks:

for (i in 1:length(covpatient)){

    a <- names(covpatient[i])
    b <- sum(covpatient[[i]]$cov == 0)
    c <- sum(covpatient[[i]]$cov > 0 & covpatient[[i]]$cov <= 40)
    d <- sum(covpatient[[i]]$cov > 40 & covpatient[[i]]$cov <= 100)
    e <- sum(covpatient[[i]]$cov > 100)
    summary <- c(a,b,c,d,e)

}

So for every dataframe in the list covpatient, I want to create a summary variable which consists of 5 elements (a,b,c,d,e). Then I want to make a new data.frame which stores all summary values (5 columns & i rows).

Could someone give me a hand?

Arun · Accepted Answer · 2013-01-28 13:32:59Z

4

One way is to use lapply with rbind and then call as.data.frame. Since there is no data to play with, I'll give the general idea.

o <- lapply(1:length(covpatient), function(i) {
    a <- names(covpatient[i])
    b <- sum(covpatient[[i]]$cov == 0)
    c <- sum(covpatient[[i]]$cov > 0 & covpatient[[i]]$cov <= 40)
    d <- sum(covpatient[[i]]$cov > 40 & covpatient[[i]]$cov <= 100)
    e <- sum(covpatient[[i]]$cov > 100)
    c(a,b,c,d,e)
})
out <- as.data.frame(do.call(rbind, o))

edited Jan 28, 2013 at 13:32

answered Jan 28, 2013 at 12:43

Arun

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2 Comments

user1987607 Over a year ago

Yes, that I understand. But when I try to run it, it says: "Error unexpected symbol in: " out"

Dinre Over a year ago

Arun has the exact answer to your question. Using 'lapply' over the set and then binding will do what you want. I have a feeling, though, that this could be done more simply by backing up a few steps and arranging your data differently. This feels like something that should be done with an aggregation package like 'plyr', 'data.table', or even 'SPARQL'.

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