I have a column in my dataframe and this is bit odd.

when I do a class(df$Contributor) it shows that its a dataframe , dataframe whithin a dataframe ?? :(

```
> class(df$Contributor)
[1] "data.frame"
>

```

Is there any way I could change this to a factor ?

Here's a partial output from str(df1)

```
$ ArticleId  : Factor w/ 186 levels "10.1002/ajh.26",..: 167 24 130 136 5 15 20 179 175 70 ...
 $ Volume     : Factor w/ 93 levels "10","100","103",..: NA 12 NA 67 NA NA NA NA NA 18 ...
 $ Issue      : Factor w/ 14 levels "1","10","11",..: NA 11 NA 9 NA NA NA NA NA 8 ...
 $ Members    :'data.frame':    186 obs. of  1 variable:
  ..$ Contributor: chr  "Ellis Johnson A, Hernandez John , Erin Martin D, Doe Jane M" "Ibrahim Joseph A" "Tenzen E M, Zhao V, Jahn T, Lee S J, McCarthy P L, Izzo J D, Romi M, Drexler R, Dlesch S, Tim H, Atamandi N, Lee E, Persuzo"| __truncated__ "Croso, Tim Zi, Gram Lindsey R, Jackson Samuel J, Friedman Tom A, Johnson Boris J, Johnson Alan "| __truncated__ ...

```

I tried doing 

```
df$Contributor <- as.factor(df$Contributor)

```

I got an error

```
Error in sort.list(y) : 'x' must be atomic for 'sort.list'
Have you called 'sort' on a list?

```