List/Set.lookup("key")

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List.lookup("key")

The command .lookup() It is intended for look-up tables (i.e. single dimension arrays). For the key value is supplied, the matched key's value is return. We can set up an example listing, using a List-type attribute:

$MyList = "ant:Wood ant;bee:Carder bee;cow:Jersey;dog:Labrador" 

This creates a 4 item look-up list. The first list item has two parts - the key 'ant' and its paired value 'Wood ant'. Passing a key via .lookup, returns its key:

$MyString = $MyList.lookup("cow"); → "Jersey", as list item 3's key is matched.

If a key value with no match is passed, the result is an empty string

$MyString = $MyList.lookup("pig"); → ""

But if we add a 'default' key/value pair (anywhere in the list):

$MyList = "ant:Wood ant;bee:Carder bee;cow:Jersey;dog:Labrador;default:animal" 

and re-run the last example:

$MyString = $MyList.lookup("pig"); → "animal"

There is still no match but as a default is defined, the default value of "animal" is returned.

More complex and nuanced use of .lookup() is described in the discussion of look-up tables.

Legacy use (pre v8)

For look-up tables .lookup() is preferred to the older .at() for clarity, and to avoid ambiguity when the argument is numeric. Using the example list as above:

$MyString = $MyList.at(3); → "dog:Labrador", the whole fourth element of the list (don't forget N is counted from zero).

$MyString = $MyList.lookup(3) → "animal", the lookup result for key value 5 which doesn't exist, so we get the default.