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Editorial Team
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Asked: 2026-06-04T16:07:17+00:00

How do I append data frames one after the other to form another data

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How do I append data frames one after the other to form another data frame?
Whether a data frame would be included or not will be decided by a criteria.

Here is an example data:

d1 <- data.frame(MyGroups =sample(LETTERS,100,replace=TRUE),
                 MyInt = sample(c(1:20),100,replace=TRUE))

Now, how should I choose groups (A,B,C…) from MyGroups that have mean of variable MyInt greater than 10?

I tried the following without a success. Here, I am appending the data frame into a file based on the given criteria.

require("plyr")

keepGrp <- function(df0) { 
  if(max(df0$MyInt < 10)) {df0 <- NULL}
  write.csv(df0,'mytable.txt',append=TRUE,sep=',')
}

ddply(d1,.(MyInt),function(x) keepGrp(x))

The desired data frame should be in file mytable.txt
I am fully sure there is a better way to do what I am trying to do.
I would be happy to clarify my question if I need to do so.
I will appreciate of someone can (1) show me a feedback on improving my programming thoughts (2) give me a solution to my problem.

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1 Answer

  1. Editorial Team

    If I understand your question properly, you want to calculate the mean by group and only write those that meet a certain threshold to a pre-existing file. If so, why not calculate all the means at once, subset that, then write that out? Here’s a one liner that should probably be split into multiples, but I think you’ll get the point:

    write.table(
  subset(
    ddply(d1, "MyGroups", transform, meanval = mean(MyInt)
          ), 
    meanval > 10), 
  "yourcsv.csv", append = TRUE, sep = ",", col.names = FALSE
  )
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