[R] set dataframe field value from lookup table

[David Winsemius]

On Dec 9, 2010, at 10:51 AM, Jon Erik Ween wrote:

> Thanks David
>
> What I am trying to do is set up a script that assigns z-scores to a  
> large dataframe (2500x300, but has Age in years and test scores as  
> columns.) from a published table of age-corrected standard scores on  
> this cognitive test.
>
> 1) The age intervals in the lookup table are given and not my choice.

You may want to skip the intermediate translation to the row and  
column labels and just use the results of findInterval:

 >  findInterval( 16, c(0, 17, 19, 24, 29, 34, 44, 54, 64, 69, 74, 79,  
84, 89) )
[1] 1
 >  findInterval( 90, c(0, 17, 19, 24, 29, 34, 44, 54, 64, 69, 74, 79,  
84, 89) )
[1] 14

Those look like appropriate indices for the column argument
>
> 2) Sorry I didn't post an example table, it looks something like  
> this ("Age" is in the first row, standard scores in the first column):
>
>        17   19   24   29   34   44 ....
> 30   2.6  2.6  2.6  2.6  2.6  2.6
> 29  1.8  1.8  1.8  2.0  2.6  2.6
> 28  1.0  1.0  1.8  1.8  2.6  2.6
> 27  0.0  0.5  1.0  1.8  2.6  2.6
> 26   -.5  0.0  0.0  1.0  1.8  2.6
> .
> .
> .
> .
>
> So, if a subject (row) has age==29 and a standard score of 28, the  
> value should be 1.8, etc.

Looks like a job for two findInterval indices to be used used with  
"[ r , c ] ".

-- 
David.

>
> Thanks
>
>
> Jon
>
> Soli Deo Gloria
>
> Jon Erik Ween, MD, MS
> Scientist, Kunin-Lunenfeld Applied Research Unit
> Director, Stroke Clinic, Brain Health Clinic, Baycrest Centre
> Assistant Professor, Dept. of Medicine, Div. of Neurology
>    University of Toronto Faculty of Medicine
>
> Kimel Family Building, 6th Floor, Room 644
> Baycrest Centre
> 3560 Bathurst Street
> Toronto, Ontario M6A 2E1
> Canada
>
> Phone: 416-785-2500 x3648
> Fax: 416-785-2484
> Email: jween at klaru-baycrest.on.ca
>
>
> Confidential: This communication and any attachment(s) may contain  
> confidential or privileged information and is intended solely for  
> the address(es) or the entity representing the recipient(s). If you  
> have received this information in error, you are hereby advised to  
> destroy the document and any attachment(s), make no copies of same  
> and inform the sender immediately of the error. Any unauthorized use  
> or disclosure of this information is strictly prohibited.
>
>
>
> On 2010-12-09, 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 
>>> $Age>=19,19,17))))))))))))
>>
>> Ew, painful. If you want categorized ages (since what the above  
>> coding is producing is not "rounded" in any sense of that word as I  
>> understand it, then why not findInterval() as an index into the  
>> ages you wnat to label these case with?
>>
>> df$Agetmp <- c(17,19,24,29,34,44,54,64,69,74,79,84)[  # note  
>> Extract operation
>>            findInterval(runif(100,0,100),  
>> c(17,19,24,29,34,44,54,64,69,74,79,84,110) )
>>           ]  # close extraction
>>
>>
>> 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
>>
>

David Winsemius, MD
West Hartford, CT