R: Sampling function to select a maximum number of dates per...

thinDates {rcarbon}

R Documentation

Sampling function to select a maximum number of dates per site, bin or phase.

Description

Function to select a subset of uncalibrated radiocarbon dates up to a maximum sample size per site, bin or phase.

Usage

thinDates(ages, errors, bins, size, thresh = 0.5, method = "random", seed = NA)

Arguments

`ages`	A vector of uncalibrated radiocarbon ages
`errors`	A vector of uncalibrated radiocarbon errors (same length as ages)
`bins`	A vector of labels corresponding to site names, ids, bins or phases (same length as ages)
`size`	A single integer specifying the maximum number of desired dates for each label stated bin.
`thresh`	A single numeric value between 0 and 1 specifying the approximate proportion (after rounding) of the resulting sample that will be chosen according to lowest date errors. At the extremes, O produces a simple random sample whereas 1 selects the sample dates with the lowest errors. Ignored if method="random".
`method`	The method to be applied where "random" simple selects a random sample, whereas "splitsample", picks some proportion (see thresh) of the sample to minimise errors, and randomly samples the rest. At present, these are the only two options.
`seed`	Allows setting of a random seed to ensure reproducibility.

Value

A numeric vector of the row indices corresponding to those of the input data.

Examples

data(euroevol)
foursites <- euroevol[euroevol$SiteID %in% c("S2072","S4380","S6139","S9222"),]
table(as.character(foursites$SiteID))
## Thin so each site has 10 dates each max, with random selection
thinInds<- thinDates(ages=foursites$C14Age, errors=foursites$C14SD, 
bins=foursites$SiteID, size=10, method="random", seed=123)
tdates <- foursites[thinInds,]
tdates
## Same but choose the first 60% (i.e. 6 dates) from the lowest errors 
## and then fill in the rest randomly.
thinInds<- thinDates(ages=foursites$C14Age, errors=foursites$C14SD, 
bins=foursites$SiteID, size=10, method="splitsample", thresh=0.6, seed=123)
tdates1 <- foursites[thinInds,]
tdates1