[R] preserving date formats in functions

[jween]

Hi there!

I have two date columns in a dataframe I need to selectively collapse based
on missing values and which date comes first (imported from an text file).
This is what I did:

RHSSP$CT<- as.POSIXct(RHSSP$CT, 
format='%m/%d/%y %H:%M')
RHSSP$MRI   <- as.POSIXct(RHSSP$MRI, 
format='%m/%d/%y %H:%M')
RHSSP$Scan  <-
ifelse(is.na(RHSSP$MRI),RHSSP$CT,ifelse(is.na(RHSSP$CT),RHSSP$MRI,ifelse(RHSSP$CT>RHSSP$MRI,RHSSP$MRI,RHSSP$CT)))

RHSSP$CT and RHSSP$MRI remain properly formatted (e.g.: "2011-06-21 22:31:00
PDT") BUT RHSSP$Scan does not (e.g.: 1294076700)

I can't figure out how to maintain the proper format during the replacement.
Looks like the replacement inherits the ifelse comparison format.

Any suggestions?

Many thanks

Jon

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[R] subset columns from list with variable substitution

[jween]

Hi there, I would like to use a list variable to select columns in a subset
from a parent table:

I have a data frame "table" with column headers a,b,c,d,e,x,y,z

and list variables

list1=c("a","b","c","d")
list2=c("a","b","x",y","z")
namelist=c("peter","paul","mary","jane")
group1=c("peter","paul")
group2=c("mary","jane")

I would like to subset "table" based on the list variable in a for loop:

for (i %in% namelist){
 if (i %in% group1){table2<-subset(table, select=list1)}
 else {{table2<-subset(table, select=list2)}
}

the "select=list1" syntax does not work. What would be the correct way to do
this?

Many Thanks

Jon

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Re: [R] subset columns from list with variable substitution

[jween]

Thanks Don

but 

table[,list1]

did not work either:

Error in `[.data.frame`(table, , list1) : undefined columns selected.

I'm guessing my list (list1) is not structured right? Displaying it has no
commas, so the whole list may be taken as a single variable rather than a
sequence of variables? I've tried various ways of reformatting (c(),
as.list(), etc), but no go.

also

"i in namelist" does not work while
"i %in% namelist" does. I don't really reference "i" in any function, only
using it in the conditional. 


Any other suggestions?

Thanks

Jon

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