Look Within the First Element of a List for Replacement Values

This is a helper function used by some seawater functions (with names starting with sw) to facilitate the specification of water properties either with distinct arguments, or with data stored within an oce object that is the first argument.

Usage

lookWithin(list)

Arguments

list

A list of elements, typically arguments that will be used in sw functions.

Value

A list with elements of the same names but possibly filled in from the first element.

Details

If list[1] is not an oce object, then the return value of lookWithin is the same as the input value, except that (a) eos is completed to either "gsw" or "unesco" and (b) if longitude and latitude are within list[1], then they are possibly lengthened, to have the same length as the first item in the data slot of list[1].

The examples may clarify this somewhat.

Examples

# 1. If first item is not a CTD object, just return the input
lookWithin(list(a = 1, b = 2)) # returns a list
#> $a
#> [1] 1
#> 
#> $b
#> [1] 2
#> 
# 2. Extract salinity from a CTD object
data(ctd)
str(lookWithin(list(salinity = ctd)))
#> List of 1
#>  $ salinity: num [1:181] 29.9 29.9 29.9 29.9 29.9 ...
# 3. Extract salinity and temperature. Note that the
# value specified for temperature is ignored; all that matters
# is that temperature is named.
str(lookWithin(list(salinity = ctd, temperature = NULL)))
#> List of 2
#>  $ salinity   : num [1:181] 29.9 29.9 29.9 29.9 29.9 ...
#>  $ temperature: num [1:181] 14.2 14.2 14.2 14.2 14.2 ...
# 4. How it is used by swRho()
rho1 <- swRho(ctd, eos = "unesco")
rho2 <- swRho(ctd[["salinity"]], ctd[["temperature"]], ctd[["pressure"]], eos = "unesco")
stopifnot(all.equal(rho1, rho2))