missing

Function

  missing — test for the "missing" error

Synopsis

missing(val: any) -> bool

Description

The missing function returns true if its argument is error("missing") and false otherwise.

This function is often used to test if certain fields do not appear as expected in a record, e.g., missing(a) is true either when this is not a record or when this is a record and the field a is not present in this.

It's also useful in shaping when applying conditional logic based on the absence of certain fields:

switch (
  case missing(a) => ...
  case missing(b) => ...
  default => ...
)

Examples

echo '{foo:10}' | zq -z 'yield {yes:missing(bar),no:missing(foo)}' -
echo '{foo:[1,2,3]}' | zq -z 'yield {yes:has(foo[3]),no:has(foo[0])}' -
echo '{foo:{bar:"value"}}' |
  zq -z 'yield {yes:missing(foo.baz),no:missing(foo.bar)}' -
echo '{foo:10}' | zq -z 'yield {yes:missing(bar+1),no:missing(foo+1)}' -
echo 1 | zq -z 'yield missing(bar)' -
echo '{x:error("missing")}' | zq -z 'yield missing(x)' -

=>

{yes:true,no:false}
{yes:false,no:true}
{yes:true,no:false}
{yes:true,no:false}
true
true