R: How can I append multiple rows to a data.frame during a loop?

Question

I discovered that it seems that I can not add rows to a data.frame in place.

The following code is a minimal example which should append a new row to the data.frame every iteration, but it does not append any.

Please note, in reality I have a complex for-loop with a lot of different if-statements and depending on them I want to append new different data to different data frames.

df <- data.frame(value=numeric()) 

appendRows <- function(n_rows) {
  for(i in 1:n_rows) {
    print(i)
    df <- rbind(df, setNames(i,names(df)))
  }
}
appendRows(10) #Does not append any row, whereas "df <- rbind(df, setNames(1,names(df)))" in a single call appends one row.

How can rows be added to a data.frame in place?

Thanks :-)

Change to df <<- rbind(df, setNames(i,names(df))). (see Scope) — GKi
– GKi, Commented Jan 14, 2020 at 12:50
Does this answer your question? R function not returning values — camille
– camille, Commented Jan 14, 2020 at 14:11

Clemsang · Accepted Answer · 2020-01-14 13:19:38Z

1

Don't forget to return your object:

df <- data.frame(value=numeric())

appendRows <- function(n_rows) {
  for(i in 1:n_rows) {
    print(i)
    df <- rbind(df, setNames(i,names(df)))
  }
  return(df)
}
appendRows(10)

To modify df you have to store it:

df <- appendRows(10)

answered Jan 14, 2020 at 13:19

Clemsang

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