Having trouble adding new elements to my hash (Ruby) - ruby

Question

new to Ruby, new to coding in general...
I'm trying to add new elements into my hash, incrementing the value when necessary. So I used Hash.new(0) and I'm trying to add new values using the "+=" symbol, but when I do this I get an error message -
"/tmp/file.rb:6:in `+': String can't be coerced into Integer (TypeError)
from /tmp/file.rb:6:in `block in stockList'
from /tmp/file.rb:3:in `each'
from /tmp/file.rb:3:in `each_with_index'
from /tmp/file.rb:3:in `stockList'
from /tmp/file.rb:24:in `<main>'
"
Here's my code:
def stockList(stock, cat)
hash = Hash.new(0)
stock.each_with_index do |word, i|
if cat.include?(word[i])
char = word[i]
hash[char] += num(word)
end
end
new_arr = []
hash.each do |k, v|
new_arr.push(k,v)
end
return new_arr
end
def num(word)
nums = "1234567890"
word.each_char.with_index do |char, i|
if nums.include?(char)
return word[i..-1]
end
end
end
puts stockList(["ABAR 200", "CDXE 500", "BKWR 250", "BTSQ 890", "DRTY 600"], ["A", "B"])
Does anyone know why this is happening?
It's a codewars challenge -- I'm basically given two arrays and am meant to return a string that adds the numbers associated with the word that starts with the letter(s) listed in the second array.
For this input I'm meant to return " (A : 200) - (B : 1140) "

Answer 1

Your immediate problem is that num(word) returns a string, and a string can't be added to a number in the line hash[char] += num(word). You can convert the string representation of a numeric value using .to_i or .to_f, as appropriate for the problem.
For the overall problem I think you've added too much complexity. The structure of the problem is:
Create a storage object to tally up the results.
For each string containing a stock and its associated numeric value (price? quantity?), split the string into its two tokens.
If the first character of the stock name is one of the target values,
update the corresponding tally. This will require conversion from string to integer.
Return the final tallies.
One minor improvement is to use a Set for the target values. That reduces the work for checking inclusion from O(number of targets) to O(1). With only two targets, the improvement is negligible, but would be useful if the list of stocks and targets increase beyond small test-case problems.
I've done some renaming to hopefully make things clearer by being more descriptive. Without further ado, here it is in Ruby:
require 'set'
def get_tallies(stocks, prefixes)
targets = Set.new(prefixes) # to speed up .include? check below
tally = Hash.new(0)
stocks.each do |line|
name, amount = line.split(/ +/) # one or more spaces is token delimiter
tally[name[0]] += amount.to_i if targets.include?(name[0]) # note conversion to int
end
tally
end
stock_list = ["ABAR 200", "CDXE 500", "BKWR 250", "BTSQ 890", "DRTY 600"]
prefixes = ["A", "B"]
p get_tallies(stock_list, prefixes)
which prints
{"A"=>200, "B"=>1140}
but that can be formatted however you like.

Answer 2

The particular issue triggering this error is that your def num(word) is essentially a no-op, returning the word without any change.
But you actually don't need this function: this...
word.delete('^0-9').to_i
... gives you back the word with all non-digit characters stripped, cast to integer.
Note that without to_i you'll still receive the "String can't be coerced into Integer" error: Ruby is not as forgiving as JavaScript, and tries to protect you from results that might surprise you.
It's a codewars challenge -- I'm basically given two arrays and am
meant to return a string that adds the numbers associated with the
word that starts with the letter(s) listed in the second array.
For this input I'm meant to return " (A : 200) - (B : 1140) "
This is one way to get there:
def stockList(stock, cat)
hash = Hash.new(0)
stock.each do |word|
letter = word[0]
if cat.include?(letter)
hash[letter] += word.delete('^0-9').to_i
end
end
hash.map { |k, v| "#{k}: #{v}" }
end
Besides type casting, there's another difference here: always choosing the initial letter of the word. With your code...
stock.each_with_index do |word, i|
if cat.include?(word[i])
char = word[i]
... you actually took the 1st letter of the 1st ticker, the 2nd letter of the 2nd ticker and so on. Don't use indexes unless your results depend on them.

Answer 3

stock = ["ABAR 200", "CDXE 500", "BKWR 250", "BTSQ 890", "DRTY 600"]
cat = ["A", "B"]
I concur with your decision to create a hash h with the form of Hash::new that takes an argument (the "default value") which h[k] returns when h does not have a key k. As a first step we can write:
h = stock.each_with_object(Hash.new(0)) { |s,h| h[s[0]] += s[/\d+/].to_i }
#=> {"A"=>200, "C"=>500, "B"=>1140, "D"=>600}
Then Hash#slice can be used to extract the desired key-value pairs:
h = h.slice(*cat)
#=> {"A"=>200, "B"=>1140}
At this point you have all the information you need to display the result any way you like. For example,
" " << h.map { |k,v| "(#{k} : #{v})" }.join(" - ") << " "
#=> " (A : 200) - (B : 1140) "
If h before h.slice(*cat) is large relative to h.slice(*cat) you can reduce memory requirements and probably speed things somewhat by writing the following.
require 'set'
cat_set = cat.to_set
#=> #<Set: {"A", "B"}>
h = stock.each_with_object(Hash.new(0)) do |s,h|
h[s[0]] += s[/\d+/].to_i if cat_set.include?(s[0])
end
#=> {"A"=>200, "B"=>1140}