Hello,

I have two series, one with stream stage measurements every 5 minutes, and
the other with barometric pressure measurements every hour.  I want to
subtract each barometric pressure measurement from the 12 stage measurements
closest in time to it (6 stage measurements on either side of the hour).

I want to do something like the following, but I don't know the syntax.

"If the Julian day of the stage measurement is equal to the Julian day of
the pressure measurement, AND the absolute value of the difference between
the time of the stage measurement and the hour of the pressure measurement
is less than or equal to 30 minutes, then subtract the pressure measurement
from the stage measurement (and put it in a new column in the stage data
frame)."

                     if ( stage$julian_day = baro$julian_day & |stage$time -
baro$hour| <= 30 )
                     then (stage$stage.cm - baro$pressure)

Can you help me?

Thanks,
JL

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