Delete nested hash according to key => value - ruby

Question

I have this hash:
response = '{"librairies":[{"id":1,"books":[{"id":1,"qty":1},{"id":2,"qty":3}]},{"id":2,"books":[{"id":1,"qty":0},{"id":2,"qty":3}]}]}'
in which I'd like to delete every librairies where, at least, one of the book quantity is null.
For instance, with this given response, I'd expect this return:
'{"librairies":[{"id":1,"books":[{"id":1,"qty":1},{"id":2,"qty":3}]}]}'
I've tried this:
parsed = JSON.parse(response)
parsed["librairies"].each do |library|
library["books"].each do |book|
parsed.delete(library) if book["qty"] == 0
end
end
but this returns the exact same response hash, without having deleted the second library (the one with id => 2).

Answer 1

You can use Array#delete_if and Enumerable#any? for this
# Move through each array element with delete_if
parsed["librairies"].delete_if do |library|
# evaluates to true if any book hash in the library
# has a "qty" value of 0
library["books"].any? { |book| book["qty"] == 0 }
end
Hope this helps

Answer 2

To avoid changing the hash parsed, you could do the following.
Firstly, let's format parsed so we can see what we're dealing with:
parsed = { "libraries"=>[ { "id"=>1,
"books"=>[ { "id"=>1, "qty"=>1 },
{ "id"=>2, "qty"=>3 } ]
},
{ "id"=>2,
"books"=>[ { "id"=>1, "qty"=>0 },
{ "id"=>2, "qty"=>3 } ]
}
]
}
Later I want to show that parsed has not been changed when we create the new hash. An easy way of doing that is to compute a hash code on parsed before and after, and see if it changes. (While it's not 100% certain that different hashes won't have the same hash code, here it's not something to lose sleep over.)
parsed.hash
#=> 852445412783960729
We first need to make a "deep copy" of parsed so that changes to the copy will not affect parsed. One way of doing that is to use the Marshal module:
new_parsed = Marshal.load(Marshal.dump(parsed))
We can now modify the copy as required:
new_parsed["libraries"].reject! { |h| h["books"].any? { |g| g["qty"].zero? } }
#=> [ { "id"=>1,
# "books"=>[ { "id"=>1, "qty"=>1 },
# { "id"=>2, "qty"=>3 }
# ]
# }
# ]
new_parsed # => { "libraries"=>[ { "id"=>1,
"books"=>[ { "id"=>1, "qty"=>1},
{ "id"=>2, "qty"=>3}
]
}
]
}
And we confirm the original hash was not changed:
parsed.hash
#=> 852445412783960729