How to append rows to an R data frame

Question

I have looked around StackOverflow, but I cannot find a solution specific to my problem, which involves appending rows to an R data frame.

I am initializing an empty

Answer 1

A more generic solution for might be the following.

    extendDf <- function (df, n) {
    withFactors <- sum(sapply (df, function(X) (is.factor(X)) )) > 0
    nr          <- nrow (df)
    colNames    <- names(df)
    for (c in 1:length(colNames)) {
        if (is.factor(df[,c])) {
            col         <- vector (mode='character', length = nr+n) 
            col[1:nr]   <- as.character(df[,c])
            col[(nr+1):(n+nr)]<- rep(col[1], n)  # to avoid extra levels
            col         <- as.factor(col)
        } else {
            col         <- vector (mode=mode(df[1,c]), length = nr+n)
            class(col)  <- class (df[1,c])
            col[1:nr]   <- df[,c] 
        }
        if (c==1) {
            newDf       <- data.frame (col ,stringsAsFactors=withFactors)
        } else {
            newDf[,c]   <- col 
        }
    }
    names(newDf) <- colNames
    newDf
}

The function extendDf() extends a data frame with n rows.

As an example:

aDf <- data.frame (l=TRUE, i=1L, n=1, c='a', t=Sys.time(), stringsAsFactors = TRUE)
extendDf (aDf, 2)
#      l i n c                   t
# 1  TRUE 1 1 a 2016-07-06 17:12:30
# 2 FALSE 0 0 a 1970-01-01 01:00:00
# 3 FALSE 0 0 a 1970-01-01 01:00:00

system.time (eDf <- extendDf (aDf, 100000))
#    user  system elapsed 
#   0.009   0.002   0.010
system.time (eDf <- extendDf (eDf, 100000))
#    user  system elapsed 
#   0.068   0.002   0.070