CODEWITHSUNDEEP
r
Elizabeth
Elizabeth

Reputation: 13

Adding a column to a dataframe within a function not working

I'm trying to add a column to a dataframe within a function and when I run it I don't get any errors but the column is not in the dataframe in the global environment. This is my code:

scale.it<-function(df,var,newvar){
  varn<-as.numeric(df[[var]])
  last<-max(varn)
  #df[[newvar]]<-varn/last
  return(df[[newvar]]<-varn/last)
}
scale.it(go.cubs.go,"PAge","IPAge")

So essentially, I want my current dataframe go.cubs.go to have all of the current columns plus IPAge.

I know there is a scale function that already exists but I need to adapt this code later so I need to be able to add columns to dataframes in functions.

Any help is greatly appreciated!

Upvotes: 0

Views: 1471

Answers (2)

Onyambu
Onyambu

Reputation: 79208

Calling by reference/pointers is not really a thing in R though you can use the R.oo packages. One way to do it in Base R is to evaluate within the parent frame. In that case, the change will happen to the object 'pointed' to. This is mostly the workings of data.table with the function :=. Here is a simple example:

scale.it<-function(df,var,newvar){
  varn<-as.numeric(df[[var]])
  last<-max(varn)
  eval.parent(substitute(df[[newvar]]<-varn/last))
}

m = head(iris)
scale.it(m,"Sepal.Width","sss")
m
  Sepal.Length Sepal.Width Petal.Length Petal.Width Species       sss
1          5.1         3.5          1.4         0.2  setosa 0.8974359
2          4.9         3.0          1.4         0.2  setosa 0.7692308
3          4.7         3.2          1.3         0.2  setosa 0.8205128
4          4.6         3.1          1.5         0.2  setosa 0.7948718
5          5.0         3.6          1.4         0.2  setosa 0.9230769
6          5.4         3.9          1.7         0.4  setosa 1.0000000

You will notice the addition of the column sss in the original m dataframe

Upvotes: 0

Jonathan
Jonathan

Reputation: 11

As mentioned by others in the comments:

  1. Variables declared in a function are local to that function (see: Global and local variables in R)
  2. You need to assign the output of the function to a variable

Example:

# Function
scale.it<-function(df,var,newvar){
  varn<-as.numeric(df[[var]])
  last<-max(varn)
  df[[newvar]]<-varn/last
  return(df) # Return dataframe
}

# Create data frame
go.cubs.go <- data.frame('a' = sample(1:10,5, replace = TRUE),
                         'b'= sample(1:10,5, replace = TRUE),
                         'PAge'= sample(1:10,5, replace = TRUE))

# Replace original data frame (or create new one)
go.cubs.go <- scale.it(go.cubs.go, "PAge", "IPAge")

Upvotes: 1

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