bash - AWK matching values in a column and performing calculation -

i'm new @ awk , i'm trying figure out answer problem. have flat file following values:

403 | sanmateo   | f | 2015-04-09 18:50:24.38 403 | sanmateo   | t | 2015-04-09 18:45:24.36 403 | sanmateo   | t | 2015-04-09 18:40:24.383 403 | sanmateo   | f | 2015-04-09 18:35:24.357 403 | sanmateo   | t | 2015-04-09 18:30:24.355 404 | redwoodcity| f | 2015-04-09 18:35:50.308 404 | redwoodcity| t | 2015-04-09 18:30:50.242 404 | redwoodcity| f | 2015-04-09 18:25:50.245 404 | redwoodcity| t | 2015-04-09 18:20:50.242 404 | redwoodcity| f | 2015-04-09 18:15:50.242 

i want use awk compare $1 of current line $1 of next line, , $3 ~/f/. if statement true subtract $4 of next line $4 of current line , write difference in new column of current line , if false nothing. have far this:

awk 'begin {fs="|";} {if (nr $1 ~ nr++ $1 && $3 ~ /f/) subtract = nr $4 - nr++ $4; {print subtract}}' allhealthrecords_sorted 

and that's not working. can please help?

save time_diff.awk

begin {fs = "[[:blank:]]*\\|[[:blank:]]*"}  # convert "yyyy-mm-dd hh:mm:ss.fff" number function to_time(timestamp,       fraction) {     fraction = timestamp     sub(/\..*$/, "", timestamp)     gsub(/[-:]/, " ", timestamp)     sub(/.*\./, "0.", fraction)     return mktime(timestamp) + fraction }  # gawk has no builtin abs() function function abs(val) {      return( val < 0 ? -1*val : val)  }  # add time diff if condition met nr > 1 {     diff = 0     if ($1+0 == key && flag == "f")          diff = abs( to_time($4) - to_time(time) )     print line (diff > 0 ? " | " diff : "") }   {     # remember previous line's values     key = $1+0; flag = $3; time = $4; line = $0 }  end {print} 

then

$ gawk -f time_diff.awk file         403 | sanmateo| f                | 2015-04-09 18:50:24.38 | 300.02         403 | sanmateo| t                | 2015-04-09 18:45:24.36         403 | sanmateo| t                | 2015-04-09 18:40:24.383         403 | sanmateo| f                | 2015-04-09 18:35:24.357 | 300.002         403 | sanmateo| t                | 2015-04-09 18:30:24.355         404 | redwoodcity| f                | 2015-04-09 18:35:50.308 | 300.066         404 | redwoodcity| t                | 2015-04-09 18:30:50.242         404 | redwoodcity| f                | 2015-04-09 18:25:50.245 | 300.003         404 | redwoodcity| t                | 2015-04-09 18:20:50.242         404 | redwoodcity| f                | 2015-04-09 18:15:50.242