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Vex

#N/A: no value is available

#N/A means that a value is not available. A field is missing, or a reduction has no values to work with. A spreadsheet gives the same code when a lookup finds no match.

A field that the record does not haveorigin
app("add", ref("position"), ref("mass"))
step 3 of 3

Result at A: #N/A the record at "A" has no value at "mass"

originABCD
result#N/A missing-field#N/A missing-field#N/A missing-field#N/A missing-field

The program adds the field mass to the position. The boxes have no field mass, so the reference fails at each origin. The op add then gives the same error, because one failed argument gives its own error.

Kinds

Section titled “Kinds”
Kind Cause
missing-field The record has no value at the path, or the value is null. The segments __proto__, constructor and prototype are not fields, and they also give this kind.
empty min, max, mean or first of an empty list. Also reduce of an empty list, with an op that has no identity.

Why the types do not prevent it

Section titled “Why the types do not prevent it”

from(p) accepts only the fields of the record type. But a space can hold records of different shapes. The builder merges their types, so a field of one record can be missing in another record. root.field(path) reads any dotted path, with a type that you give.

An axis with a where test can also give an empty list at some origins. Thus #N/A is a value that a program must expect.

The fix

Section titled “The fix”
  • Read a field that each record has.
  • Give a fallback with ifError, for example root.from("mass").ifError(1).
  • For an empty list, use count() or sum(), which give 0. Or give reduce an op with an identity.

Refer to error values for the other codes.