[Rd] Manipulating R lists in C

[Roger Bivand]

On Fri, 17 Nov 2006, Tom McCallum wrote:

> Hi,
> 
> I have been studying the R manual on lists but cannot seem to create a  
> simple R list in C - I keep on getting "'dimnames' applied to non-array"  
> whenever I attempt to assign names to the list elements:

Maybe:

   setAttrib( priceList, R_NamesSymbol, dimnames );

why should a list have dimnames?

In addition, your dimnames is a list, and likely ought to be a character 
vector. That way you can get away with many fewer PROTECT().

Roger

> 
> Wanted output a list structure something like
> 	[ type="Bid", price=2.0, volume=1000 ]
> 
> I can get up to a list of
> 	[ "Bid2, 2.0, 1000 ]
> 
> But for the life of me I can't assign the names to the list items - any  
> suggestions?
> 
> Below is what I already have - any comments on things I don't really need  
> to do as well in terms of creating extra string objects etc are also  
> helpful.
> 
> Many thanks
> 
> Tom
> 
> 
> ======EXTRACT=========
> 
> 
>    SEXP typeStr, volumeStr, priceStr, typeValStr;
>    SEXP priceList;
> 
>    // create main list of vectors (unspecific items )
>    PROTECT( priceList = allocVector( VECSXP, 3 ) );
> 
>    // for each item create a label and attach value
>    PROTECT( typeValStr = allocVector( STRSXP, 1 ) );
>    SET_STRING_ELT( typeValStr, 0,  
> mkChar( getPriceDataTypeAsString( p.getData().getType() ).c_str() ) );
>    SET_STRING_ELT( priceList, 0, typeValStr) ;
> 
>    SEXP priceSXP;
>    PROTECT( priceSXP = allocVector( REALSXP, 1) );
>    REAL(priceSXP)[0] = p.getData().getPrice();
>    SET_VECTOR_ELT( priceList, 1, priceSXP);
> 
>    SEXP volumeSXP;
>    PROTECT( volumeSXP = allocVector( REALSXP, 1 ) );
>    REAL(volumeSXP)[0] = p.getData().getVolume();
>    SET_VECTOR_ELT( priceList, 2, volumeSXP);
> 
>    ********WORKS UP TO HERE*************
> 
>    // add the names of the list items (type,price,volume)
>    SEXP dimnames;
>    PROTECT( dimnames = allocVector( VECSXP, 3 ) );
> 
>    // first create string objects
>    PROTECT( typeStr = allocVector( STRSXP,1 ) );
>    SET_STRING_ELT( typeStr, 0, mkChar("type") );
> 
>    PROTECT( priceStr = allocVector( STRSXP,1 ) );
>    SET_STRING_ELT( priceStr, 0, mkChar("price") );
> 
>    PROTECT( volumeStr = allocVector( STRSXP,1 ) );
>    SET_STRING_ELT( volumeStr, 0, mkChar("volume") );
> 
>    // assign string objects to vector
>    SET_VECTOR_ELT( dimnames, 0, typeStr );
>    SET_VECTOR_ELT( dimnames, 1, priceStr);
>    SET_VECTOR_ELT( dimnames, 2, volumeStr );
> 
>    // assign vector to original list of data
>    setAttrib( priceList, R_DimNamesSymbol, dimnames ); <----- I think this  
> is wrong but I don;t know what it should be
> 
> ===========END EXTRACT===============
> 
> 

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no