R help - May 2013 - how to read numeric vector as factors using read.table.ffdf

I have a big data set that includes character variables of many different
values. I'm trying to use ff to read the data and then use biglm.big.matrix
to build linear models. However, since big.matrix will convert all
character vectors to factors and the character labels will be lost. I
decided to create a lookup table outside of R for my character columns and
use numbers to represent different levels for R. However, I do not know how
to tell read.table.ffdf these columns should be considered factors instead
of numerics. Please help. thanks.

	[[alternative HTML version deleted]]

Please read the posting guide.

Your question is far from clear. First you're apparently unhappy because
character vectors are being converted to factors. Then later you ask how
to tell a function that some numeric datas should be considered factors.
Which is it that you want? A simple short example would help.
> help.search('read.table.ffdf')
No vignettes or demos or help files found with alias or concept or title
matching 'read.table.ffdf' using regular expression matching.
> help.search('biglm.big.matrix')
No vignettes or demos or help files found with alias or concept or title
matching 'biglm.big.matrix' using regular expression matching.

You need to provide information about where these apparent functions come
from. 

Regardless, if after using read.table.ffdf you have a data frame, you can
convert any column, numeric or character, to a factor using the factor()
function. You can also convert factors back to characters using, for
example, format().

In other 'read' functions, such as read.table, when character data is
converted to factors, the "labels" are not lost. Perhaps the
documentation
for read.table.ffdf describes how to prevent conversion to factor.

-Don


-- 
Don MacQueen

Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062





On 5/7/13 3:46 PM, "li li" <zgscgh01 at gmail.com> wrote:
>I have a big data set that includes character variables of many different
>values. I'm trying to use ff to read the data and then use
>biglm.big.matrix
>to build linear models. However, since big.matrix will convert all
>character vectors to factors and the character labels will be lost. I
>decided to create a lookup table outside of R for my character columns and
>use numbers to represent different levels for R. However, I do not know
>how
>to tell read.table.ffdf these columns should be considered factors instead
>of numerics. Please help. thanks.
>
>	[[alternative HTML version deleted]]
>
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>and provide commented, minimal, self-contained, reproducible code.