Group (K): Difference between revisions

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(Created page with ":''This page is about the K primitive that returns a dictionary. For the primitive that returns an array introduced by BQN, see Group (BQN).'' {{Built-in|Group|<nowiki>=</nowiki>}} is a monadic function in K that returns a dictionary whose keys are the unique values in its argument and whose value for a given key is the list of indices where it appears. In versions before K4, which introduced dictionaries, Group returns only an array of the index lis...")
 
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:''This page is about the K primitive that returns a dictionary. For the primitive that returns an array introduced by BQN, see [[Group (BQN)]].''
{{Built-in|Group|<nowiki>=</nowiki>}} is a [[monadic function]] in [[K]] that returns a [[dictionary]] whose keys are the [[unique]] values in its argument and whose value for a given key is the list of indices where it appears. In versions before K4, which allowed dictionaries with arbitrary keys, Group returns only an array of the index lists, and the keys must be obtained separately.
 
{{Built-in|Group|<nowiki>=</nowiki>}} is a [[monadic function]] in [[K]] that returns a [[dictionary]] whose keys are the [[unique]] values in its argument and whose value for a given key is the list of indices where it appears. In versions before K4, which introduced dictionaries, Group returns only an array of the index lists, and the keys must be obtained separately.


Group can be seen as a simplified version of [[Key]], as it contains the same information as <syntaxhighlight lang=apl inline>{⍺⍵}⌸</syntaxhighlight>: the first result column is the dictionary keys and the second is its values. The [[BQN]] primitive also called [[Group (BQN)|Group]] can be described as a specialization of K's Group to arrays, where an array corresponds to a dictionary with natural numbers for its keys.<ref>[[Marshall Lochbaum]]. [https://mlochbaum.github.io/BQN/commentary/history.html#group BQN's development history: Group].</ref>
Group can be seen as a simplified version of [[Key]], as it contains the same information as <syntaxhighlight lang=apl inline>{⍺⍵}⌸</syntaxhighlight>: the first result column is the dictionary keys and the second is its values. The [[BQN]] primitive also called [[Group (BQN)|Group]] can be described as a specialization of K's Group to arrays, where an array corresponds to a dictionary with natural numbers for its keys.<ref>[[Marshall Lochbaum]]. [https://mlochbaum.github.io/BQN/commentary/history.html#group BQN's development history: Group].</ref>

Latest revision as of 23:29, 17 March 2024

=

Group (=) is a monadic function in K that returns a dictionary whose keys are the unique values in its argument and whose value for a given key is the list of indices where it appears. In versions before K4, which allowed dictionaries with arbitrary keys, Group returns only an array of the index lists, and the keys must be obtained separately.

Group can be seen as a simplified version of Key, as it contains the same information as {⍺⍵}⌸: the first result column is the dictionary keys and the second is its values. The BQN primitive also called Group can be described as a specialization of K's Group to arrays, where an array corresponds to a dictionary with natural numbers for its keys.[1]

External links

References

  1. ↑ Marshall Lochbaum. BQN's development history: Group.
APL built-ins [edit]
Primitives (Timeline) Functions
Scalar
Monadic Conjugate ∙ Negate ∙ Signum ∙ Reciprocal ∙ Magnitude ∙ Exponential ∙ Natural Logarithm ∙ Floor ∙ Ceiling ∙ Factorial ∙ Not ∙ Pi Times ∙ Roll ∙ Type ∙ Imaginary ∙ Square Root ∙ Round
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Non-Scalar
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Quad names Index origin ∙ Comparison tolerance ∙ Migration level ∙ Atomic vector
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