Merging and updating hash keys in Redis with Ruby - ruby

Question

I have a list the following hashes:
{
key_main1: {
k1: 1,
k2: 11,
k3: 33,
k4: 146,
k5: 12,
# etc
},
key_main2: {
k1: 1,
k2: 11,
k3: 33,
k4: 146,
k5: 12,
# etc
},
# etc
}
which is save in a redis as json:
redis_key1 = "redis_key1"
redis.set("redis_key", my_hash.to_json)
redis.get("redis_key") # =>
"{"key_main":{"k1":1,"k2":11,"k3":33,"k4":146,"k5":12}}"
The hashes have the same structure but can have different keys. On each iteration I want to update the existing keys by summing up the values of "k"s or/and insert the keys that don't exist:
So the second hash in the list looks like this
{
key_main1: {
k3: 44,
k4: 14,
k18: 99
},
key_main3: {
k2: 77
}
}
Then after the seconds iteration the result in Redis will look like the following:
{
key_main1: {
k1: 1,
k2: 11,
k3: 33,
k4: 160,
k5: 12,
k18: 99
},
key_main2: {
k1: 1,
k2: 11,
k3: 33,
k4: 146,
k5: 12
},
key_main3: {
k2: 77
}
}
What's the easiest and best way to do it? Do I have to parse (restore)json in each iteration in order to check if the keys exist and update or insert them?

Answer 1

The best way is to parse the JSON back into a hash, otherwise you will have a really hard time figuring out how to combine the hashes.
To combine them, the best and easiest is with Hash#merge:
h1 = { m1: { k1: 10, k2: 20, k3: 30 }, m2: { k1: 11, k2: 12 } }
h2 = { m1: { k1: 500, k2: 5, k4: 40 }, m3: { k2: 123 } }
pp h1.merge(h2) { |key, v1, v2|
v1.merge(v2) { |key, v1, v2| v1 + v2 }
}
=> { :m1 => { :k1 => 510,:k2 => 25, :k3 => 30, :k4 => 40 },
:m2 => { :k1 => 11, :k2 => 12},
:m3 => { :k2 => 123 } }
This code assumes the keys in h1 and h2 always contain a hash with integer keys.