[R] approxfun asymmetry

[Timothy Earl (Cefas)]

Hi,

I'm seeing an asymmetry in how approxfun treats -Inf and Inf, which I don't understand from reading the help file.

e.g. a simple step function
tmp <- approxfun(x=c(-Inf, -0.2, 0.2,  Inf), y=c(-1, -1, 1, 1))
tmp(c(-1, 0, 1))
# [1] NaN   0   1
I expected: # [1] -1   0   1

Clearly I can work round this by using type=2, and not specifying the end points (or by replacing -Inf by a large negative number), but I was wondering what I was missing about the different behaviour between positive and negative infinity.

To simplify further:
approxfun(x=c(-1000,  Inf), y=c(1, 1))(0)
# [1] 1

approxfun(x=c(-Inf,  1000), y=c(1, 1))(0)
# [1] NaN

Sessioninfo:
R version 4.3.0 (2023-04-21 ucrt) -- "Already Tomorrow"
Copyright (C) 2023 The R Foundation for Statistical Computing
Platform: x86_64-w64-mingw32/x64 (64-bit)

Thanks,

Tim
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