[R] set dataframe field value from lookup table

[David Winsemius]

On Dec 9, 2010, at 10:33 AM, David Winsemius wrote:

>
> On Dec 9, 2010, at 9:34 AM, Jon Erik Ween wrote:
>
>>
>> Hi
>>
>> This is (hopefully) a bit more cogent phrasing of a previous post.  
>> I'm
>> trying to compute a z-score to rows in a large dataframe based on  
>> values in
>> another dataframe. Here's the script (that does not work). 2  
>> questons,
>>
>> 1) Anyone know of a more elegant way to calculate the "rounded" age  
>> value
>> than the nested ifelse's I've used?
>>
>> 2) how to reference the lookup table based on computed indices?
>>
>> Thanks
>>
>> Jon
>>
>> # Define tables
>> DSTzlook <-
>> read.table("/Users/jween/Documents/ResearchProjects/ABC/data/ 
>> DSTz.txt",
>> header=TRUE, sep="\t", na.strings="NA", dec=".", strip.white=TRUE)
>> df<-stroke
>>
>> # Compute rounded age.
>> df$Agetmp
>> <-ifelse(df$Age>=89,89,ifelse(df$Age>=84,84,ifelse(df 
>> $Age>=79,79,ifelse(df$Age>=74,74,ifelse(df$Age>=69,69,ifelse(df 
>> $Age>=64,64,ifelse(df$Age>=54,54,ifelse(df$Age>=44,44,ifelse(df 
>> $Age>=34,34,ifelse(df$Age>=29,29,ifelse(df$Age>=24,24,ifelse(df 
>> $Age>=19,19,17))))))))))))
>
> Ew, painful. If you want categorized ages (since what the above  
> coding is producing is not "rounded" in any sense of that word as I  
> understand it, then why not findInterval() as an index into the ages  
> you wnat to label these case with?
>
> ### Cut out incorrect code from prior posting:

c(17, 17, 19, 24, 29, 34, 44, 54, 64, 69, 74, 79, 84, 89)[
        findInterval( 19, c(0, 17, 19, 24, 29, 34, 44, 54, 64, 69, 74,  
79, 84, 89) ) ]

I see my pasting of a test vector didn't get properly replaced. Also  
added the missing "89" and fixed the mis-registration of "label  
vector" with interval vector. (This reply was better tested than the  
first, but you clearly need to check my work here.)
-- 
David
>
>
>
> The other option, of course, and a more "honest" one in this  
> instance would be
>
> cut(vec, breaks=c(...), labels=c(...) )
>
> (It's not clear why you are not picking midpoint ages within those  
> brackets to me.)
>
>>
>> # Reference the lookup table based on computed indices
>> df$DSTz
>> <-DSTzlook[which(DSTzlook[,1]==df$Agetmp),which(DSTzlook[1,]==df$DSF 
>> +df$DSB)]
>
> I have not been able to figure out what you are trying to do here.  
> Trying to use a 2d lookup looks promising a a way to emulate what an  
> Excel user might attempt, but an example (as requested in the  
> message at the bottom of every posting) would really be of great  
> help in making this more concrete for those of us with insufficient  
> abstractive abilities.
>
> -- 
> David.
>
>>
>> # Cleanup
>> #rm(df)
>> #df$Agetmp<-NULL
>> -- 
>> View this message in context: http://r.789695.n4.nabble.com/set-dataframe-field-value-from-lookup-table-tp3080245p3080245.html
>> Sent from the R help mailing list archive at Nabble.com.
>>
>
>
> David Winsemius, MD
> West Hartford, CT
>
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David Winsemius, MD
West Hartford, CT