Averaging across groups

Run this example using its test data from within FlightPath Data.

~
  This csvpath finds the average temp for all days sampled in each month.
  The result is a "month_ave" dictionary with an average temp keyed by
  each observed month number.

  I.e. for the first three months of the year you might see:
	{'01': 27.25, '02': 34.25, '03': 39.65}

  While this kind of pivot may be useful, it's worth pointing out that
  CsvPath Framework's goal is to assess the validity of data and upgrade
  it, if needed, to ideal-form raw data. Analysis and reporting are
  valuable, but ancillary.

  test-data: temps.txt
~
$[1*][
	~ find the month number ~
	@month = regex(/[0-9]{4}-([0-9]{1,2})/, #0, 1)

	~ count the number of samples we have for the month ~
	tally.month_obs(@month)

	~ get a subtotal of the month's temps ~
	@sub = subtotal.month_temp(@month, #temp)

	~ get the count of observations in month ~
	@obs = get("month_obs_month",@month)

	~ get the average for the month ~
	@ave = divide(@sub, @obs)

	~ store the average ~
	put("month_ave", @month, @ave)

print("
   temp: $.headers.temp
   obs: $.variables.obs
   average: $.variables.ave
   month_temp: $.variables.month_temp
   month_ave: $.variables.month_ave
")
]