R/fastingProxyByDay.R

In MRCIEU/GLU: Derives Summary Variables from Continuous Glucose Monitoring (CGM) data

# The MIT License (MIT)
# Copyright (c) 2018 Louise AC Millard, MRC Integrative Epidemiology Unit, University of Bristol
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# For each valid day in validDays, derive the fasting proxy SG - the mean of the 30 minutes with the lowest SG values.
# Returns a data frame of the fasting proxy for each day, and the average across all days overall
fastingProxyByDay <- function(validDays) {

	nocts = c()

	# column names for each auc value we generate	
	cnames = c()

	count=1

	# for each valid day, calculate the auc
	for (vd in validDays) {

		nt = getDayGlucoseValues(vd, night=TRUE)
		
		# nocturnal mean of 3 lowest consecutive values of this day only
		noctVD = fastingProxy(nt)
		nocts = append(nocts, noctVD)

		cnames = append(cnames, paste("fastingproxy_day", count, sep=""))
                count=count+1
	}

	# set column names for auc values
	res = rbind(nocts)
	colnames(res) = cnames

	# average across days
	nocAv = meanAcrossDays("fastingproxy_day", res)
  	othervars = rbind(c(nocAv))
	colnames(othervars) = c("meanFastingProxyPerDay")

	res = cbind(res, othervars)
	return(res)

}