Create a function which will make a list of dataframes through subsetting a dataframe in R

Question

I'm trying to write a function which will subset a dataframe for me, according to different lengths of time (number of months); and create a list of new dataframes which are all slightly different subsets. I want to be able to apply this function to any data.

Here is an example of what I'm trying to do.

month <- c(0:35)
product<- c(112:147)
index <- rnorm(36)
originaldata <- data.frame(month, product, index)

sset <-  function(df, time, length, windows) {

  #Create the subset rule
  subfun <- function(x,y,z) {  x[x[[y]] >= z & x[[y]] <= z+length-1,] }

  #Apply this rule to dataframe 
  regdfs <- lapply(1:windows, 
    function(j) {subfun(x = df, y = time, z = j - 1) }) 
  }

#Apply sset function to create dataframe subsets
camsets <- sset(df = originaldata, time = originaldata$month, length = 13, windows = 24)

When I run this code, I get a variety of error messages.

This is the link to my original question, which was helpfully answered (thanks Carl), Create a list of a list of dataframes, by subsetting a list of dataframes in R . This time I'm trying to write a function to do this, and I'm probably doing something stupid.

Any help much appreciated, thanks.

It would help if you expanded on "a variety of error messages". — r2evans
– r2evans, Commented Mar 9, 2017 at 1:44
Sorry about that. The latest error message is Error in .subset2(x, i, exact = exact) : attempt to select less than one element in integerOneIndex . Thanks for your help. — Laura
– Laura, Commented Mar 9, 2017 at 2:00
First, x[[y]] can only retrieve a single column of a data.frame, but you are passing a vector in y; perhaps you mean x[y,]? Second, y is 0-based, but vectors in R are 1-based, so you are likely not getting back what you want. — r2evans
– r2evans, Commented Mar 9, 2017 at 2:05
Update: I'm now getting the error message In Ops.factor(left, right) : ‘<=’ not meaningful for factors . Any ideas? Thanks. — Laura
– Laura, Commented Mar 9, 2017 at 2:29

tjjjohnson · Accepted Answer · 2017-03-09 20:55:38Z

0

Using split as suggested by waterling

month <- c(0:35)
product <- c(112:147)
index <- rnorm(36)
originaldata <- data.frame(month, product, index)

createsubsets <- function(df, length, windows) {
  cutoffs <-seq(0,windows*length,length)
  originaldata$group <- cut(originaldata$month, cutoffs,include.lowest=TRUE )
  split(originaldata, originaldata$group)
}

camsets <- createsubsets(df, 13, 24)

edited Mar 9, 2017 at 20:55

answered Mar 9, 2017 at 2:39

tjjjohnson

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