python - Shuffling combinations without converting iterable (itertools.combinations) to list -

-

the following simple code gives me possible combinations of length 3 of 200 elements.

from itertools import combinations comb = combinations( range(200), 3 )

i want combinations in random order in order pick first n combinations. however, if convert comb list , shuffle following, may memory error because list might contain many elements:

comb = list(comb) # might huge , give memory error  random.shuffle(comb) n = 10 comb = comb[:10] # first n random combinations

is there other way n random combinations ? (i.e., not in order generated itertools.combinations).

there c(200, 3) = 1313400 possible combinations. mentioned, number can out of hand due combinatorial explosion. example, if choose 4 instead of 3 elements, number of combinations approximately 50 times larger (64684950). instead of randomly selecting these combinations, can randomly build possible combinations.

to build combinations, can use random.sample random library. random.sample(range(200), 3) randomly generate 1 of 1313400 combinations. if call again, generate combination.

there 2 issues:

  1. order important in random.sample ([1, 2, 3] different [1, 3, 2]). in combinations, not. solve that, can use sorted().
  2. random.sample independently generate next 3 numbers. therefore, combinations generated in different iterations same. although unlikely example (≈0.0000343), can use set store combinations unique combinations stored.

the following generate 10 different combinations:

import random combs = set() n = 10 while len(combs) < n:     combs.add(tuple(sorted(random.sample(range(200), 3))))

Comments

Post a Comment

Popular posts from this blog

Django REST Framework perform_create: You cannot call `.save()` after accessing `serializer.data` -

-
i have following viewset: class artistprofileviewset(viewsets.modelviewset): queryset = artistprofile.objects.all() serializer_class = artistprofileserializer def perform_create(self, serializer): if serializer.is_valid(): serializer.save() with following serializers: class simpleartisttrackserializer(serializers.hyperlinkedmodelserializer): class meta: model = artisttrack fields = (...my fields...) class artistprofileserializer(serializers.hyperlinkedmodelserializer): owners = userserializer(many=true, required=false) tracks = simpleartisttrackserializer(many=true, required=false) class meta: model = artistprofile fields = (...my fields...) i getting following error: assertionerror: cannot call `.save()` after accessing `serializer.data`.if need access data before committing database inspect 'serializer.validated_data' instead. i don't see editing serializer.data object. th...
Read more

Why does Go error when trying to marshal this JSON? -

-
i'm trying rather simple example of trying decode json file structs using golang. however, when attempting error that json: cannot unmarshal object go value of type []main.track which don't understand. here's code in question, , json can found here . package main import ( "encoding/json" "fmt" "net/http" "os" ) // tracks group of track types type tracks struct { tracks []track } // track represents singular track type track struct { name string url string artist artist } // artist represents single artist type artist struct { name string mbid string url string } func main() { url := "http://ws.audioscrobbler.com/2.0/?method=geo.gettoptracks&api_key=c1572082105bd40d247836b5c1819623&format=json&country=netherlands" response, err := http.get(url) if err != nil { fmt.printf("%s\n", err) os.exit(1) } de...
Read more