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Is there a neat way of looking up the key of a dictionary by an atom value if that atom is inside a value list ?
Assumption: The value lists of the dictionary have each unique elements
Example:
d:`tech`fin!(`aapl`msft;`gs`jpm) / would like to get key `fin by looking up `jpm
d?`gs`jpm / returns `fin as expected
d?`jpm / this doesn't work unfortunately
$[`jpm in d`fin;`fin;`tech] / this is the only way I can come up with
The last option does not scale well with the number of keys
Thanks!
991
Below example shows a multi-level nested list in kdb+, we can use over (/) in conjunction with “raze” to converge on a flat list. But instead of having to use “raze” multiple times to flatten the nested list, we can instead use raze combined with /. Raze will keep executing until it has flattened the entire nested structure.
Nested lists have item (s) that are themselves lists. The number of levels of nesting for a list is called its depth. Informally, the depth measures how much repeated indexing is necessary to arrive at only atoms. Atoms have depth 0 and simple lists have depth 1. The notation of complex lists is reflected in nested parentheses.
Kdb+/q originated as an obscure academic language but over the years, it has gradually improved its user friendliness. K (1993, crisp version of A+, developed by A. Whitney) Why? − If you need a single solution for real-time data with analytics, then you should consider kdb+.
Get the item at index 1 from L, and from it retrieve the item at index 2, and from it retrieve the item at index 0. There is an alternate notation for repeated indexing into the constituents of a nested list. The last retrieval can also be written as, Assignment via index also works at depth.
You can take advantage of how where operates with dictionaries, and use in :
where `jpm in/:d
,`fin
Note this will return a list, so you might need to do first on the output if you want to replicate what you have above.
181
Why are you making this difficult on yourself? Use a table!
q)t:([] c:`tech`tech`fin`fin; sym:`aapl`msfw`gs`jpm)
q)first exec c from t where sym=`jpm
You can of course do what you're asking:
first where `jpm in'd
but this doesn't extend well to vectors while the table-approach does!
q)exec c from t where sym in `jpm`gs
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