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pythonlambdarethinkdbrethinkdb-python
iraycd
iraycd

Reputation: 892

Multiple filter using lambda in python on rethinkdb?

I am trying to filter the array object inside a table. Here is a case where I have filtered and it works perfectly.

tags = ["school", "hollywood"]
tagsLambda =  lambda post: (post["tags"].contains(tags[0])) | (post["tags"].contains(tags[1]))
d = r.db("test").table("posts").filter(
    tagsLambda
).run()

But, My question is I am doing the lambda operation manually, instead I want tagsLambda to filter all the tags. How do I do it?

Upvotes: 2

Views: 442

Answers (2)

Nizam Mohamed
Nizam Mohamed

Reputation: 9220

tags = ["school", "hollywood"]
tagsLambda =  lambda post: ( 
eval('|'.join(
           [r'(post["tags"].contains("' + tag + '"))' for tag in tags]
    ))
)
d = r.db("test").table("posts").filter(tagsLambda).run()

[ r'post["tags"].contains("' + tag + '")' for tag in tags ] is a list comprehension. It builds a list of strings like (post["tags"].contains("school")) for each tag in tags. The '|'.join operation builds a string from the list of strings with '|' in between like (post["tags"].contains("school")) | (post["tags"].contains("hollywood")). eval evaluates the whole string.

The above code can be simplified using reduce as 

tags = ["school", "hollywood"]
tagsLambda =  lambda post:
    reduce(lambda x,y: x | y, [ post["tags"].contains(tag) for tag in tags])

d = r.db("test").table("posts").filter(tagsLambda).run()

For Python 3, 'functools' has to be imported to use reduce and replace reduce with functools.reduce.

The second lambda can be replaced with a function. 

import operator as op
reduce(op.or_, [ post["tags"].contains(tag) for tag in tags])

User generators for better result. 

reduce(op.or_, ( post["tags"].contains(tag) for tag in tags))

Upvotes: 1

gunn
gunn

Reputation: 9165

I think you should be able to do something like this:

tags = ["school", "hollywood"]
r.db("test").table("posts").filter(
  lambda post: post["tags"].contains(lambda tag:
    r.expr(tags).contains(tag)
  )
).run(conn)

See http://rethinkdb.com/api/python/contains/

Upvotes: 3

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