CODEWITHSUNDEEP
hashtableracket
Octa9on
Octa9on

Reputation: 182

Add parallel lists of keys and values to a hash table in Racket?

I have a list of keys and a list of values that I want to add to a hash table. The best I've got so far is:

(apply hash-set*! table (flatten (map list keys values)))

But that makes a lot of nested lists only to flatten them.

Is there a simple way to do this without making the nested lists?

Upvotes: 0

Views: 621

Answers (3)

rnso
rnso

Reputation: 24623

Simplest 'for' loop can be used here: 

(for ([k keys]
      [v vals])
  (hash-set! table k v))

Upvotes: 1

John Clements
John Clements

Reputation: 17233

I think I would write it like this:

#lang racket

(define keys '(a b c))
(define values '(1 2 3))
(define table (hash 'p 34 'c 9))

(for/fold ([ht table])
          ([k (in-list keys)]
           [v (in-list values)])
  (hash-set ht k v))

... no extra consing required.

Upvotes: 1

Sylwester
Sylwester

Reputation: 48775

Unless your lists are tens of thousands long it really doesn't matter but in the name of laziness here is what I would have done:

(require srfi/26) ; cut

(for-each (cut hash-set! table <> <>) keys vals)

Same without SRFI-26:

(for-each (λ (k v) (hash-set! table k v)) keys vals)

Upvotes: 1

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