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_. Indeterminate Noun
Indeterminate (_.) is a numeric atom. It is a placeholder broadly comparable with NaN (not a number). See: WikiPedia:NaN and Essays/Indeterminate.
It can appear in data imported from external sources, eg from a DLL or data base package. For an exhaustive list of sources see the entry in the J Dictionary.
If a computation produces NaN when the arguments were not NaN, J will signal a NaN error. If a NaN is an argument to a computation, it is undefined what the result value is: it could be NaN or any other value.
Some computations that produce NaN according to the IEEE standard do not produce NaN in J:
- 0 * _ = 0
- 0 * __ = 0
- 0 % 0 = 0
- 0 ^ 0 = 1
- _ ^ 0 = 1
- 1 ^ _ = 1
p=: _ [ q=: __ p+q |NaN error | p +q p%q |NaN error | p %q 0*p,q 0 0 1%q 0
Common uses
Indeterminate (_.) is not recommended for use in J computations. It signifies a "missing value" in statistical data. You should detect it using 128!:5 and replace it at the first opportunity with a proper numeric value suited to the computation you want to perform, eg (0), (_) or (__).
z 1 2 _. 4 128!:5 z 0 0 1 0 0 (I. 128!:5 z) } z NB. replace missing values with ZERO 1 2 0 4
More Information
Indeterminate is the only numeric atom that is not equal to itself. Further bizarre properties arise from this fact.
See Essays/Indeterminate.
z=: 1 2 _. 4 1+z 2 3 _. 5 z=z 1 1 0 1 +/z _.
Numbers (".) can take a left argument. This specifies a numeric atom to replace any ill-formed numbers. This (together with 3!:n) are the only ways to force _. to arise in pure-J code. But it is not recommended for the purpose! Use (0) or Infinity (_) instead.
z=: '.2 0.2 2.45 3E56 3F56 _1 _0 77'
NB. (".) accepts non-J-numerals like '.2' and '3E56' but not '3F56' ...
".z
|ill-formed number
| ".z
_. ".z
0.2 0.2 2.45 3e56 _. _1 0 77
0 ".z NB. replace bad-numerals by ZERO
0.2 0.2 2.45 3e56 0 _1 0 77
_ ".z NB. replace bad-numerals by INFINITY
0.2 0.2 2.45 3e56 _ _1 0 77