Select hash from collection of hash based on subset of another hash - ruby

Question

Given I have hash:
Grp1:
key1: value1
key2: value2
key3: value3
Grp2:
key1: value4
key2: value2
key3: value5
and I have another hash:
key1: value4
key2: value2
I want to search in first set of hash and choose Grp2' key1:value4 because Grp2 matches the condition. How should I do that?
Note: I tried using the select command and tried some logic offered by referring documents. My intentions are not to get sample code but just a hint. Sorry if my question sounds like I am asking for code.

Answer 1

What you refer to as your first hash is not hash. In fact, it's not a Ruby object of any kind. If it is to be a hash, you need to write it like this:
g = { :Grp1 => { key1: value1, key2: value2, key3: value3 },
:Grp2 => { key1: value4, key2: value2, key3: value5 } }
Since the keys are all symbols, you could instead use the syntax:
g = { Grp1: { key1: value1, key2: value2, key3: value3 },
Grp2: { key1: value4, key2: value2, key3: value5 } }
value1 (and value2 and so on) must be either a variable or a method, but you have not given us it's value (if it's a variable) or its return value is (if it's a method), so I will replace those variables or methods with literals:
g = { Grp1: { key1: 7, key2: 4, key3: 'cat' },
Grp2: { key1: 1, key2: 3, key3: 'dog' } }
Your second hash:
h = { :key1 => value4, :key2 => value2 }
has the same problem, so I'll replace it with:
h = { :key1 => 1, :key2 => 3 }
which alternatively could be expressed:
h = { key1: 1, key2: 3 }
Assuming what I have written is correct, we can write a method as follows, using the methods Hash#keys, Hash#key?, Enumerable#find and Enumerable#all?:
def doit(g, h)
hkeys = h.keys
puts "hkeys=#{hkeys}"
g.find do |k,v|
puts "k=#{k}"
puts "v=#{v}"
hkeys.all? do |j|
puts " v.key?(#{j})=#{v.key?(j)}"
puts " v[#{j}]==#{h[j]}: #{v[j]==h[j]}"
v.key?(j) && v[j] == h[j]
end
end
end
I've added some puts statements so you can see the results of the calculations. For g and h defined above (with literal values):
doit(g,h)
hkeys=[:key1, :key2]
k=Grp1
v={:key1=>7, :key2=>4, :key3=>"cat"}
v.key?(key1)=true
v[key1]==1: false
k=Grp2
v={:key1=>1, :key2=>3, :key3=>"dog"}
v.key?(key1)=true
v[key1]==1: true
v.key?(key2)=true
v[key2]==3: true
#=> [:Grp2, {:key1=>1, :key2=>3, :key3=>"dog"}]
After stripping out the puts statements and making one small change, I would write the method like this:
def doit(g, h)
hkeys = h.keys
g.find { |_,v| hkeys.all? { |j| v.key?(j) && v[j] == h[j] } }
end
The small change is that I've replaced the block variable k with the variable _ to draw attention to the fact that I'm not using it in the block.
There are many ways to to write this method. Here's another, using the method Hash#values_at:
def doit(g, h)
hkeys = h.keys
hvalues = h.values
g.find { |_,v| v.values_at(*hkeys) == hvalues }
end