Lookup By Key

The most fundamental dictionary operation: given a key, retrieve its value.

Single and Multiple Key Lookup

prices:`AAPL`MSFT`GOOG!185.25 410.10 142.80

prices[`MSFT]        / 410.1   — index syntax
prices`MSFT          / 410.1   — juxtaposition syntax

prices[`AAPL`GOOG]   / 185.25 142.8  — multiple keys at once

Indexing with a list of keys returns a list of values in the same order — lookups are naturally vectorised.

Performance: the Unique Attribute

For small dictionaries, lookup speed is rarely a concern. For dictionaries with many thousands or millions of keys, applying the unique attribute (`u#) to the key vector lets q build an internal hash table, turning lookups into roughly constant-time operations instead of a linear search:

syms:`u#`AAPL`MSFT`GOOG`TSLA`NVDA
prices:syms!185.25 410.10 142.80 238.50 875.20

This is a standard optimisation for large reference-data dictionaries — symbol lookups, instrument metadata, exchange mappings — where the key set is known to be unique.