pushing a value into an array within a hash - arrays

Question

Ive been working at this code for a radix sort for awhile now. Everything has seemed to be coming together fine until i try to push a value into an array within a hash.
Im getting an error message that the value is nil, however ive checked all the values in question just prior to trying to store them in the array and its still not allowing me to do so. Any ideas? buckets[sdigit].push(num) is the line that tells me one of my values is nil.
arr = []
while arr.size < 100
arr.push(rand(1000))
end
for outer_index in arr
puts "for outer index(#{outer_index} in arr"
buckets = Hash.new()
puts "buckets = Hash.new()"
puts "for j in 0..9"
for j in 0..9
buckets[j.to_s] = Array.new()
#buckets[j.to_s] = [j]
puts "buckets[j.to_s(#{buckets[j.to_s]})"
end
for inner_index in arr
puts "for inner_index(#{inner_index}) in arr"
num = inner_index
puts "num(#{num}) = inner_index(#{inner_index})"
sdigit = num.to_s[-1]
puts "sdigit(#{sdigit}) = num.to_s[-1](#{num.to_s[-1]})"
digit = sdigit.to_i
puts "digit(#{digit}) = sdigit.to_i(#{sdigit.to_i})"
puts "buckets[digit] = #{buckets[sdigit]}"
puts "#{buckets["1"]}"
puts "o#{num}"
puts buckets
buckets[sdigit].push(num)
puts "buckets[digit].push(num)(#{buckets[digit].push(num)})"
end
arr = buckets.values.flatten
end `

Answer 1

buckets[sdigit].push(num) is the line that tells me one of my values
is nil.
If you look at the error message :
top.rb:30:in `block (2 levels) in <main>': undefined method `push' for nil:NilClass (NoMethodError)
and your code :
you see that line 30 is the puts, not buckets[sdigit].push(num).
Cause : there is a discrepancy between the values displayed by the puts and those used by the expression : [digit] instead of [sdigit], and that's the trace which causes the error.
Personally I write the puts traces before the statement to trace, because it shows the values that will be used by the expression before the statement which could cause the error is executed. It usually helps ... except when the trace itself is in error.
I have slightly rearranged your code :
arr = []
100.times { arr << rand(1000) }
puts arr.join(', ')
arr.each do | outer_index |
puts "===== for outer_index=#{outer_index} in arr"
buckets = Hash.new()
puts "buckets = Hash.new()"
puts "for j in 0..9"
(0..9).each do | j |
buckets[j.to_s] = Array.new()
#buckets[j.to_s] = [j]
puts "buckets[#{j.to_s}]=#{buckets[j.to_s]}"
end
arr.each do | inner_index |
puts "----- for inner_index=#{inner_index} in arr"
num = inner_index
puts "num(#{num}) = inner_index(#{inner_index})"
sdigit = num.to_s[-1]
puts "sdigit(#{sdigit}) = num.to_s[-1](#{num.to_s[-1]})"
digit = sdigit.to_i
puts "digit(#{digit}) = sdigit.to_i(#{sdigit.to_i})"
puts "buckets[digit] = #{buckets[sdigit]}"
puts "#{buckets["1"]}"
puts "o#{num}"
puts buckets
puts "buckets[sdigit].push(num)=buckets[#{sdigit}].push(#{num})"
buckets[sdigit].push(num)
# puts "buckets[digit].push(num)(#{buckets[digit].push(num)})"
end
arr = buckets.values.flatten
end