[datatable-help] Two short questions about the operation of data table

[Arunkumar Srinivasan]

DTNEW <- DT[ , {
if (all(start <= opening)){
result <- list(start, end, t.dif= unclass(round(difftime(end, start)/365.25,1)), value)
} else {
result <- list(start, end, t.dif= 20, value)
}
result}, by=ID]

Why can I not keep the column names?
When we do:

DT[, list(x, y), by=z]
the j-expression returns an unnamed list. But we understand it as a straightforward list() scenario and extract the symbols and assign them as names in output/result.

But what happens within { ... } is more complicated and therefore is hard to extract the names to set names in result.

DTNEW <- DT[ , {
if (all(start <= opening)){
result <- list(start, end, t.dif= unclass(round(difftime(end, start)/365.25,1)), value)
} else {
result <- list(start, end, t.dif= 20, value)
}
result[!(t.dif == value)]}, by=ID]

But R does not find the variable t.dif !!
But result is a list. You should be doing result[!result$t.dif == value]. That is:

DTNEW <- DT[ , {  
   if (all(start <= opening)){  
     result <- list(start, end,  t.dif= unclass(round(difftime(end, start)/365.25,1)), value)  
     } else {  
     result <- list(start, end,  t.dif= 20, value)
     }  
     result[!result$t.dif == value]}, by=ID]


Arun

From: Frank S. <f_j_rod at hotmail.com>
Reply: Frank S. <f_j_rod at hotmail.com>>
Date: September 22, 2014 at 1:16:48 PM
To: datatable-help at lists.r-forge.r-project.org <datatable-help at lists.r-forge.r-project.org>>
Subject:  [datatable-help] Two short questions about the operation of data table  

Hello to everyone,

 

Let's consider, just by way of example, the following date and data table:

 

opening <- as.Date("1990-01-01")
DT <- data.table(ID=c(1,2,3),
    start=c("1985-01-01","1993-07-15","1993-05-17"),
    end=c("1992-05-01","1997-02-25","2002-01-01"),
    value=c(7.8, 3.2, 20.0))

 

FIRST QUESTION:

 

If I execute:

 

DTNEW <- DT[ , { 
   if (all(start <= opening)){ 
     result <- list(start, end, t.dif= unclass(round(difftime(end, start)/365.25,1)), value) 
     } else { 
     result <- list(start, end, t.dif= 20, value)
     } 
   result}, by=ID]

 

Why can I not keep the column names?

   ID                       t.dif    
1:  1 1985-01-01 1992-05-01   7.3  7.8
2:  2 1993-07-15 1997-02-25  20.0  3.2
3:  3 1993-05-17 2002-01-01  20.0 20.0

SECOND QUESTION:

 

I would want to remove rows where t.dif=value in the final result. Then, I tried:

 

DTNEW <- DT[ , { 
   if (all(start <= opening)){ 
     result <- list(start, end,  t.dif= unclass(round(difftime(end, start)/365.25,1)), value) 
     } else { 
     result <- list(start, end,  t.dif= 20, value)
     } 
   result[!(t.dif == value)]}, by=ID]

 

But R does not find the variable t.dif !!

 

Thank you for your time to all of the members of the list!!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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