Ruby: inject issue when turning array into hash

Question

a = [[1, 'a'],[2, 'b'],[3, 'c'], [4, 'd']]
a.inject({}) {|r, val| r[val[0]] = val[1]}

When I run this, I get an index error

When I change the block to

a.inject({}) {|r, val| r[val[0]] = val[1]; r}

It then works.

How is ruby handling the first inject attempt that isn't getting what I want?
Is there a better way to do this?

Answer 1

a.inject({}) { |r, val| r.merge({ val[0] => val[1] }) }

Answer 2

There is an easier way -

a = [[1, 'a'],[2, 'b'],[3, 'c'], [4, 'd']]
b = Hash[a] # {1=>"a", 2=>"b", 3=>"c", 4=>"d"}

The reason the first method isn't working, is because inject uses the result of the block as the r in the next iteration. For the first iteration, r is set to the argument you pass to it, which in this case is {}.