R: Unable to rbind more than one observation to a data frame

问题

I've used data.table to create an empty data frame but when I'm adding observations to it all the observations after the first one get coerced to NA.

First I create an empty data frame using the "stringsAsFactors = FALSE" parameter:

cards <- data.frame(Ending = character(), Owner = character(), stringsAsFactors = FALSE)
str(cards)
'data.frame':   0 obs. of  2 variables:
 $ Ending: chr 
 $ Owner : chr

I get a data frame with 0 observations and two character variables as expected.

Then I create observation 1 (not the actual code - extracted from a another data.frame DF)

newcard1 <- as.list(
   c(Ending = as.character(DF[4, "Col1"]), 
      Owner = as.character(DF[4, "Col2"]))
   )
str(newcard1)
List of 2
 $ Ending: chr "1234"
 $ Owner : chr "JOE BIDEN"

and observation 2 (not the actual code - extracted from a another data.frame DF)

newcard2 <- as.list(
  c(Ending = as.character(DF[51, "Col1"]), 
    Owner = as.character(DF[51, "Col2"]))
   )
str(newcard2)
List of 2
$ Ending: chr "5678"
$ Owner : chr "JOHN TURTURRO"

Both are a list with two character variables as shown above.

Now if I bind the first observation works

cards <- rbind(cards, newcard1)
str(cards)
'data.frame':   1 obs. of  2 variables:
  $ Ending: Factor w/ 1 level "1234": 1
  $ Owner : Factor w/ 1 level "JOE BIDEN: 1

the rbind operation has changed the observation into Factors. In addition, if I try to add any other observations, rbind won't accept any other value as valid level and coerces the values to NA:

cards <- rbind(cards, newcard2)
Warning messages:
1: In `[<-.factor`(`*tmp*`, ri, value = FALSE) :
   invalid factor level, NA generated
2: In `[<-.factor`(`*tmp*`, ri, value = FALSE) :
   invalid factor level, NA generated
str(cards)
'data.frame':  2 obs. of  2 variables:
  $ Ending: Factor w/ 1 level "1234": 1 NA
  $ Owner : Factor w/ 1 level "JOE BIDEN": 1 NA

cards
   Ending       Owner
 1 1234         JOE BIDEN
 2 <NA>         <NA>

what am I doing wrong?

来源：https://stackoverflow.com/questions/48756144/r-unable-to-rbind-more-than-one-observation-to-a-data-frame

标签

rbind