R Oddities: Strings in DataFrames

July 29, 2015
By

(This article was first published on R-Chart, and kindly contributed to R-bloggers)

Have you ever read a file into R and then encountered strange problems filtering and sorting because the strings were converted to factors?  For instance, you might think the two data frames, df and df2 below are contain the same data

> df<-data .frame="" c="" hello="" stringsasfactors="FALSE)
write.csv(df, ‘df.csv’)
df2<-read .csv="" b="" df.csv="">

But look the dimensions are different

> dim(df)
[1] 1 1
> dim(df2)
[1] 1 2

And on further analysis – they are indeed different classes:

> class(df$V1)
[1] “character”
> class(df2$V1)
[1] “factor”

This behavior is very confusing to many when first introduced to R.  Over time, I accepted it but didn’t really understand how or why it originated.   Roger Peng over at the Simply Statistics blog has a great write up on why R operates this way:

http://simplystatistics.org/2015/07/24/stringsasfactors-an-unauthorized-biography/

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