R help - Sep 2009 - Convert dataframe to array of records

I would like to convert a dataframe to an array of lists, one for every
record. A natural choide is apply as.list to the rows. However, as it seems,
as.list() automatically converts all list elements to the same datatype. Eg:

myData <- data.frame(a="foo",b=as.logical(rbinom(10,1,.5)));
apply(myData,1,as.list);

In this output, all boolean values have been converted to character strings.
I don't understand why this happens; a list does not require that every
element is of the same datatype. Is there an easy way (ie avoid for-loops
etc) to convert the dataframe to an array of records, while keeping the
datatypes for every field? 

-----
Jeroen Ooms * Dept. of Methodology and Statistics * Utrecht University 

Visit  http://www.jeroenooms.com www.jeroenooms.com  to explore some of my
current projects.





 
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> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Jeroen Ooms
> Sent: Saturday, September 05, 2009 9:20 AM
> To: r-help at r-project.org
> Subject: [R] Convert dataframe to array of records
> 
> 
> I would like to convert a dataframe to an array of lists, one 
> for every
> record. A natural choide is apply as.list to the rows. 
> However, as it seems,
> as.list() automatically converts all list elements to the 
> same datatype.
No, apply itself converts the whole data.frame to a matrix,
forcing the columns to one data type.  I think that apply()
is rarely a good tool for working with data.frames.

You will have to do something like
    rowsOfDataFrame <- function(dataframe)
lapply(seq_len(nrow(dataframe)), function(i)dataframe[i,])
or perhaps as.list(dataframe[i,]) if you really want to get rid
of the data.frame-ness.

Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap tibco.com  
> Eg:
> 
> myData <- data.frame(a="foo",b=as.logical(rbinom(10,1,.5)));
> apply(myData,1,as.list);
> 
> In this output, all boolean values have been converted to 
> character strings.
> I don't understand why this happens; a list does not require 
> that every
> element is of the same datatype. Is there an easy way (ie 
> avoid for-loops
> etc) to convert the dataframe to an array of records, while 
> keeping the
> datatypes for every field? 
> 
> -----
> Jeroen Ooms * Dept. of Methodology and Statistics * Utrecht 
> University 
> 
> Visit  http://www.jeroenooms.com www.jeroenooms.com  to 
> explore some of my
> current projects.
> 
> 
> 
> 
> 
>  
> -- 
> View this message in context: 
> http://www.nabble.com/Convert-dataframe-to-array-of-records-tp
25310023p25310023.html
> Sent from the R help mailing list archive at Nabble.com.
> 
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