Handling field types in database interaction with R -

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i use rmysql , mysql database store datasets. data gets revised or store results database well. long story short, there quite interaction between r , database in use case.

most of time use convenience functions dbwritetable , dbreadtableto write , read data. unfortunately these ignoring r data types , mysql field types. mean expect mysql date fields end in date or posix class. other way around i´d think these r classes stored corresponding mysql field type. means date should not character – i not expect distinguish between float , doubles here...

i tried use dbgetquery – same result there. there have missed when reading manual or not possible (yet) in these packages? nice work around?

edit: @mdsummer tried find more in documentation, found these disappointing lines: `mysql tables read r data.frames, without coercing character or logical data factors. while exporting data.frames, factors exported character vectors.

integer columns imported r integer vectors, except cases such bigint or unsigned integer coerced r's double precision vectors avoid truncation (currently r's integers signed 32-bit quantities).

time variables imported/exported character data, need convert these favorite date/time representation.

ok, got working solution now. here's function maps mysql field types r classes. helps in particular handling mysql field type date...

dbreadmap <- function(con,table){     statement <- paste("describe ",table,sep="")     desc <- dbgetquery(con=con,statement)[,1:2]    # strip row_names if exists because it's attribute , not real column   # otherweise causes problems row count if table has row_names col   if(length(grep(pattern="row_names",x=desc)) != 0){   x <- grep(pattern="row_names",x=desc)   desc <- desc[-x,]   }        # replace length output in brackets returned describe     desc[,2] <- gsub("[^a-z]","",desc[,2])      # building dictionary      fieldtypes <- c("int","tinyint","bigint","float","double","date","character","varchar","text")     rclasses <- c("as.numeric","as.numeric","as.numeric","as.numeric","as.numeric","as.date","as.character","as.character","as.character")      fieldtype_to_rclass = cbind(fieldtypes,rclasses)      map <- merge(fieldtype_to_rclass,desc,by.x="fieldtypes",by.y="type")     map$rclasses <- as.character(map$rclasses)     #get data     res <- dbreadtable(con=con,table)        i=1     for(i in 1:length(map$rclasses)) {         cvn <- call(map$rclasses[i],res[,map$field[i]])         res[map$field[i]] <- eval(cvn)     }       return(res) }

maybe not programming practice – i don't know better. so, use @ own risk or me improve it... , of course it's half of it: reading. i´ll find time write writing function soon.

if have suggestions mapping dictionary let me know :)


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