[R] Conditional merging in R & if then statement

[Jeff Newmiller]

1) just because you don't use sqldf doesn't make it better. merge only does the join, not the conditions, so you have to apply them after merge. Untested (you should provide a complete example):

result <- merge ( detail, pdetail, by=TDATE, suffixes=c(".a",".b") )
result <- subset ( result, STIM.a >= STIM.b and STIM.a <=MAXTIM.b ) 

You can add a select argument to subset to remove the pdetail columns.

2) if is different than ifelse ... read the Introduction to R document, and/or read the help pages on if and ifelse.
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ramoss <ramine.mossadegh at finra.org> wrote:

>1)I am wandering how the following SQL statement can be written in R
>language
>w/o using sqldf:
>create table  detail2 as
>select a.*
>from   detail a,
>       pdetail b
>where a.TDATE=b.TDATE
>and    (a.STIM >= b.STIM and a.STIM <=b.MAXTIM)
>
>2) when try if then in R it only applies to the 1st row & not to whole
>dataset like in SAS. How do you get round that?
>in SAS:
>
>data summary;
>  set all1;
>  if entry='a:prop' then pctexec=stkful/stocks*100;
>run;
>
>
>
>Thanks in advance for your help.
>
>
>
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