GAMS Special Values#

The GAMS system contains five special values: UNDEF (undefined), NA (not available), EPS (epsilon), +INF (positive infinity), -INF (negative infinity). These special values must be mapped to their R equivalents. GAMS Transfer R follows the following convention to generate the 1:1 mapping:

  • +INF is mapped to Inf

  • -INF is mapped to -Inf

  • EPS is mapped to -0.0 (mathematically identical to zero)

  • NA is mapped to a NA

  • UNDEF is mapped to NaN

GAMS Transfer R syntax is designed to quickly get data into a form that is usable in further analyses or visualization. The user does not need to remember these constants as they are provided within the class SpecialValues as SpecialValues$POSINF, SpecialValues$NEGINF, SpecialValues$EPS, SpecialValues[["NA"]], and SpecialValues$UNDEF. Some examples are shown below.

library(gamstransfer)
m <- Container$new()
x <- Parameter$new(
m, "x", c("*"),
records = data.frame(uni = paste0("i", 1:6), c(
    1, SpecialValues[["POSINF"]],
    SpecialValues[["NEGINF"]], SpecialValues[["EPS"]], SpecialValues[["NA"]],
    SpecialValues[["UNDEF"]]
)),
description = "special values"
)

The following data frame for x would look like:

> x$records
    uni value
1    i1     1
2    i2   Inf
3    i3  -Inf
4    i4     0
5    i5    NA
6    i6   NaN

The user can now easily test for specific special values in the value column of the DataFrame (returns a logical vector):

> SpecialValues$isNA(x$records$value)
[1] FALSE FALSE FALSE FALSE  TRUE FALSE

> SpecialValues$isNA(x$records$value)
[1] FALSE FALSE FALSE FALSE  TRUE FALSE

> SpecialValues$isEps(SpecialValues$EPS)
[1] TRUE

> SpecialValues$isPosInf(SpecialValues$POSINF)
[1] TRUE

> SpecialValues$isNegInf(SpecialValues$NEGINF)
[1] TRUE

> SpecialValues$isNA(SpecialValues$NEGINF)
SpecialValues$isNA

> SpecialValues$isNA(SpecialValues[["NA"]])
[1] TRUE

> SpecialValues$isUndef(SpecialValues$UNDEF)
[1] TRUE

> SpecialValues$isUndef(SpecialValues[["NA"]])
[1] FALSE

> SpecialValues$isNA(SpecialValues$UNDEF)
[1] FALSE

Note

The syntax SpecialValues$NA is not allowed in R. Therefore, to access NA, one has to use SpecialValues[["NA"]]. As shown in the example above, double bracket syntax works for other special values too.