intervalGRdiff {imageData}

Calculates the growth rates for a specified time interval

Description

Using the values of the responses, calculates the specified combination of the Absolute Growth Rates using differences (AGR), the Proportionate Growth Rates (PGR) and Relative Growth Rates using log differences (RGR) between two nominated time points.

Usage

intervalGRdiff(responses, individuals = "Snapshot.ID.Tag", 
               which.rates = c("AGR","PGR","RGR"), suffices.rates=NULL, 
               times.factor = "Days", start.times, end.times, suffix.interval, 
               data)

Arguments

responses

A character giving the names of the columns in data from which the growth rates are to be calculated.

individuals

A character giving the name(s) of the factor(s) that define the subsets of the data for which each subset corresponds to the responses for an individual.

which.rates

A character giving the growth rates that are to be calculated. It should be a combination "AGR", "PGR" and "RGR".

suffices.rates

A character giving the characters to be appended to the names of the responses in constructing the names of the columns containing the calculated growth rates. The order of the suffices in suffices.rates should correspond to the order of the elements of which.rates.

times.factor

A character giving the name of the column in data containing the factor for times at which the data was collected. Its levels will be used in calculating growth rates and should be numeric values stored as characters.

start.times

A numeric giving the times, in terms of levels of times.factor, that will give a single value for each Snapshot.ID.Tag and that will be taken as the observation at the start of the interval for which the growth rate is to be calculated.

end.times

A numeric giving the times, in terms of levels of times.factor, that will give a single value for each Snapshot.ID.Tag and that will be taken as the observation at the end of the interval for which the growth rate is to be calculated.

suffix.interval

A character giving the suffix to be appended to response to form the names of the columns containing the calculated the growth rates.

data

A data.frame containing the column from which the growth rates are to be calculated.

Details

The AGR is calculated as the difference between the values of response at the end.times and start.times divided by the difference between end.times and start.times. The PGR is calculated as the ratio of response at the end.times to that at start.times and the ratio raised to the power of the reciprocal of the difference between end.times and start.times. The RGR is calculated as the log of the PGR and so is equal to the difference between the logarithms of response at the end.times and start.times divided by the difference between end.times and start.times.

Value

A data.frame with the growth rates. The name of each column is the concatenation of (i) one of responses, (ii) one of AGR, PGR or RGR, or the appropriate element of suffices.rates, and (iii) suffix.interval, the three components being separated by full stops.

Author(s)

Chris Brien

See Also

intervalGRaverage, intervalWUI, getDates, GrowthRates, splitSplines, splitContGRdiff

Examples

data(exampleData)
Area.smooth.GR <- intervalGRdiff("Area.smooth", which.rates = c("AGR","RGR"), 
                                 start.times = 31, end.times = 35,
                                 suffix.interval = "31to35",
                                 data = longi.dat)