criteria - create interval with criterion in R -

             gdk   frist   pers       start     code  reg  prog       done  omreg 1           false  false 1941-12-23 2011-01-19 mm2001 ffg frist 2012-09-21 false 4            true  false 1943-04-04 2011-09-01 mm2001 ffg frist 2012-01-11 false 6           false   true 1944-01-27 2013-09-01 mm2001 ffg frist 2014-06-12 false 10          false  false 1944-11-01 2010-01-19 mm2001 ffg frist 2010-12-17 false 11          false  false 1945-04-21 2009-09-01 mm2001 ffg frist 2010-06-14 false 12          false   true 1945-06-13 2013-01-19 mm2001 ffg frist 2014-01-13 false 

above, have piece of head (both)

i have estimated takes 160 days students read 1 semester. , want find out students approved 160 days.

i used:

gdk<-(difftime(as.date(both$done),  as.date(both$start), units="days") < 160 & !both$omreg) 

but right want add criterion range.

variable prog = program students study here programs;

frist laraa nastk nbffk nbibk ndatk nfysk nmatk nmetk nmfik nsfyy smekk  

so if student reads frist or ndatk should <320 days

for laraa nastk nbffk nbibk nfysk nmatk nmetk nmfik nsfyy smekk

it should still <160

i want have similar column gdk true , false if students meet criteria. want them adapted criterion. how i?

just put ifelse instead of 160:

( difftime(as.date(both$done), as.date(both$start), units="days") <      ifelse(both$prog %in% c("frist", "ndatk"), 320, 160) &      !both$omreg)