Convert a vector of base 4 fractions into (truncated) decimal integer values

Converts base 4 fractions, representing the full GRTS addresses from the raster data source GRTSmaster_habitats into decimal (i.e. base 10) integer values. Before the actual conversion happens, leading digits from the full GRTS address can be discarded according to the level specified by the user. Hence, the result may correspond to the GRTS ranking at a lower spatial resolution.

convert_base4frac_to_dec(x, level)

Arguments

x	A scalar or vector of base 4 fractions, originating from the GRTSmaster_habitats data source.
level	The number of leading digits to discard from the GRTS base 4 address, i.e. from the 'xxx...' digits behind the decimal mark in the '0.xxxxxxxxxxxxx' base 4 fractions. Only values from 0 (maintain full address) to 12 (only return last digit) are sensible, as the GRTS addresses are 13 digits long.

Value

The corresponding decimal (i.e. base 10) integer scalar or vector.

Details

For example, the base 4 fraction 0.0000000000100 is converted into decimal integer 16 (= 4^2) as long as the level argument is 10 or lower (if not, it will be 0) and 0.0000000000101 is converted into either 17 ( level <= 10) or 1 (if level is 11 or 12).

Long base 4 fractions seem to be handled and stored easier than long (base 4) integers. This approach follows the one of Stevens & Olsen (2004) to represent the reverse hierarchical order in a GRTS sample.

The function works on a vector and retains NA values. As such, it can be used in raster::calc(). When writing such a raster to a file, it is recommended to use the INT4U data type (see dataType).

References

Stevens D.L. & Olsen A.R. (2004). Spatially Balanced Sampling of Natural Resources. Journal of the American Statistical Association 99 (465): 262–278. doi:10.1198/016214504000000250 .

See also

Other functions involved in processing the 'GRTSmaster_habitats' data source: convert_dec_to_base4frac(), read_GRTSmh_base4frac(), read_GRTSmh_diffres(), read_GRTSmh()

Examples

oldoption <- options(list(digits = 15, scipen = 999))
# one scalar:
convert_base4frac_to_dec(0.1010101010101, level = 0)
#> [1] 17895697
# vector, level 0:
convert_base4frac_to_dec(c(NA, 0.1010101010101), level = 0)
#> [1]       NA 17895697
# vector, level 5:
convert_base4frac_to_dec(c(NA, 0.1010101010101), level = 5)
#> [1]   NA 4369
# same vector, all sensible levels computed:
sapply(0:12, function(i) {
  convert_base4frac_to_dec(c(NA, 0.1010101010101),
    level = i
  )
})
#>          [,1]    [,2]    [,3]  [,4]  [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
#> [1,]       NA      NA      NA    NA    NA   NA   NA   NA   NA    NA    NA    NA
#> [2,] 17895697 1118481 1118481 69905 69905 4369 4369  273  273    17    17     1
#>      [,13]
#> [1,]    NA
#> [2,]     1
options(oldoption)