R help - Apr 2011 - Assign Character Value to Data Frame

Dear R Helpers,

I am trying to write a character value to the row of a data frame and am
running into a problem that I don't have when I do this for numeric
arguments.  For example, the following works just fine:
> test<-data.frame(number=numeric(1))
> test[1,]<-.5
> test
  number
1    0.5

But the following bombs out:
> hold<-data.frame(symbol=character(1))
> hold[1,]<-"NYSE:MMM"
Warning message:
In `[<-.factor`(`*tmp*`, iseq, value = "NYSE:MMM") :
  invalid factor level, NAs generated

Could someone please guide me as to what adjustment I need to make to
assign this character value to this row of the data frame?  Your help
would be very much appreciated.

--John Sparks

Hi John,

The error arises because the "hold" data frame contains factors.  This
happens by default when creating data frames with character data as
you did.  Factors have a set number of levels and new values cannot be
assigned to them that fall outside their specified levels, hence the
error.  The solution is to create all the columns in the dat frame as
character to begin with or transform them to that (or at least ensure
they are not factors).  For example:
> hold <- data.frame(symbol = character(1), stringsAsFactors = FALSE)
> hold[1, ] <- "NYSE:MMM"
> hold
    symbol
1 NYSE:MMM

See ?data.frame for details.

Hope this helps,

Josh

On Tue, Apr 12, 2011 at 11:20 AM, Sparks, John James <jspark4 at uic.edu>
wrote:
> Dear R Helpers,
>
> I am trying to write a character value to the row of a data frame and am
> running into a problem that I don't have when I do this for numeric
> arguments. ?For example, the following works just fine:
>
>> test<-data.frame(number=numeric(1))
>> test[1,]<-.5
>> test
> ?number
> 1 ? ?0.5
>
> But the following bombs out:
>
>> hold<-data.frame(symbol=character(1))
>> hold[1,]<-"NYSE:MMM"
> Warning message:
> In `[<-.factor`(`*tmp*`, iseq, value = "NYSE:MMM") :
> ?invalid factor level, NAs generated
>
> Could someone please guide me as to what adjustment I need to make to
> assign this character value to this row of the data frame? ?Your help
> would be very much appreciated.
>
> --John Sparks
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/

That column of your data frame contains a factor, rather than character
values. You don't tell us how you created the data frame, but you might
be interested in the stringsAsFactors option to data.frame() and read.table().

Or, if you do actually want a factor for that column, you can use factor()
to change the levels.

Sarah

On Tue, Apr 12, 2011 at 2:20 PM, Sparks, John James <jspark4 at uic.edu>
wrote:
> Dear R Helpers,
>
> I am trying to write a character value to the row of a data frame and am
> running into a problem that I don't have when I do this for numeric
> arguments. ?For example, the following works just fine:
>
>> test<-data.frame(number=numeric(1))
>> test[1,]<-.5
>> test
> ?number
> 1 ? ?0.5
>
> But the following bombs out:
>
>> hold<-data.frame(symbol=character(1))
>> hold[1,]<-"NYSE:MMM"
> Warning message:
> In `[<-.factor`(`*tmp*`, iseq, value = "NYSE:MMM") :
> ?invalid factor level, NAs generated
>
> Could someone please guide me as to what adjustment I need to make to
> assign this character value to this row of the data frame? ?Your help
> would be very much appreciated.
>
> --John Sparks
>
-- 
Sarah Goslee
http://www.functionaldiversity.org