R help - Sep 2009 - Conditional operation on data frame, shift/roll of vector

Conditionally, when Ind of a certain row is 1, want to get sum or delta of Val
in that row and 1 row
above.

Val	Ind                 Val	Ind  Del
10	0                    10	0    NA
11	0                    11	0    NA
13	1      ------->      13	1    24 or 2
16	0                    16	0    NA

A simple way I guess is to get shifted vector of Val (say, c(NA, 10, 11, 13)),
add to or minus from
Val, then and logically AND with Ind.

Which function provides the shift operation of the vector Val?

Also welcomed if any better way to do this. Thanks.

On Sep 26, 2009, at 11:46 AM, jiangrm wrote:
> Conditionally, when Ind of a certain row is 1, want to get sum or  
> delta of Val in that row and 1 row
> above.
>
> Val	Ind                 Val	Ind  Del
> 10	0                    10	0    NA
> 11	0                    11	0    NA
> 13	1      ------->      13	1    24 or 2
> 16	0                    16	0    NA
>
> A simple way I guess is to get shifted vector of Val (say, c(NA, 10,  
> 11, 13)), add to or minus from
> Val, then and logically AND with Ind.
?diff

 > df1<-data.frame(Val=c(10,11,13,16), Ind=c(0,0,1,0))
 > c(NA, diff(df1$Val))[df1$Ind==1]
[1] 2
>
> Which function provides the shift operation of the vector Val?
?"["   # with a suitable index vector
?lag   # for time series
>
> Also welcomed if any better way to do this. Thanks.


-- 

David Winsemius, MD
Heritage Laboratories
West Hartford, CT

On Sep 26, 2009, at 12:52 PM, David Winsemius wrote:
>
> On Sep 26, 2009, at 11:46 AM, jiangrm wrote:
>
>> Conditionally, when Ind of a certain row is 1, want to get sum or  
>> delta of Val in that row and 1 row
>> above.
>>
>> Val	Ind                 Val	Ind  Del
>> 10	0                    10	0    NA
>> 11	0                    11	0    NA
>> 13	1      ------->      13	1    24 or 2
>> 16	0                    16	0    NA
>>
>> A simple way I guess is to get shifted vector of Val (say, c(NA,  
>> 10, 11, 13)), add to or minus from
>> Val, then and logically AND with Ind.
>
> ?diff
>
> > df1<-data.frame(Val=c(10,11,13,16), Ind=c(0,0,1,0))
> > c(NA, diff(df1$Val))[df1$Ind==1]
> [1] 2
>
I suppose I ought to answer the question more fully. One approach  
using indexing, is to use the logical vector produced by  df1$Ind==1  
on both sides of an assignment operation at once to determine which of  
the values of hte above set of differences get transfered:

 > df1$Del[df1$Ind==1] <- c(NA, diff(df1$Val))[df1$Ind==1]
 > df1
   Val Ind Del
1  10   0  NA
2  11   0  NA
3  13   1   2
4  16   0  NA

ifelse might also provide a solution. Something along the lines of:

df1$Del3 <- ifelse(df1$Ind ==1, c(NA, df1$Val[2:nrow(df1)]-df1$Val[1: 
(nrow(df1)-1)]), NA)

But that seems so Baroque that I think you will agree that the  
indexing method is preferable in this question.
>>
>> Which function provides the shift operation of the vector Val?
>
> ?"["   # with a suitable index vector
> ?lag   # for time series
>
>>
>> Also welcomed if any better way to do this. Thanks.
>
>
>
> -- 
>
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT