Hello, I made a mistake and passed stringsAsFactors to the wrong function in : > df <- as.data.frame( list( x = 1:3, y = c("a", "b", "c" ), stringsAsFactors = FALSE ) ) But then : > df x y 1 1 a 2 2 b 3 3 c and : > df[["y"]] [1] a b c Levels: a b c > str( df ) 'data.frame': 3 obs. of 3 variables: $ x : int 1 2 3 $ y : Factor w/ 3 levels "a","b","c": 1 2 3 $ stringsAsFactors: logi FALSE FALSE FALSE Somehow, print.data.frame does not want to print a column named "stringsAsFactors". (I know this is a bad name for a column, but ...) Apparently, this line in format.data.frame is responsible for the mismatch: x <- do.call("data.frame", rval) Romain -- Romain Francois Professional R Enthusiast +33(0) 6 28 91 30 30 http://romainfrancois.blog.free.fr |- http://bit.ly/9aKDM9 : embed images in Rd documents |- http://tr.im/OIXN : raster images and RImageJ |- http://tr.im/OcQe : Rcpp 0.7.7