`+' nil can't be coerced into FixNum (TypeError) won't go away

Question

I'm using HTTParty to connect to stockfighter.io 's API and getting a quote of a stock, which I then extract a price per share from and append it to the end of the $averageArr array.

I'm trying to average the last five values of a constantly updating array, $averageArr, and so I thought I would make a variable sum set it to zero, add those last five values to it and then divide it by 5 to get a dynamic and changing average.

Here's my code:

require 'rubygems'
require 'httparty'
require 'json'

apikey = 'API_KEY_FOR_LOGIN_HERE'
venue = "VENUEX"
stock = "FOOBAR"

base_url = "https://api.stockfighter.io/ob/api"

account = "MY_ACCOUNT_HERE"

$averageArr = []

$counter = 0

$currAve = 0


def getQuote(stock, venue, account)

    response = HTTParty.get("https://api.stockfighter.io/ob/api/venues/#{venue}/stocks/#{stock}/quote")

    orderbook = response.parsed_response

    puts orderbook["ok"]

    return orderbook["last"]
    puts orderbook["lastTrade"]

end


def getAverage(stock, venue, account)

    $averageArr.push(getQuote(stock, venue, account))
    $counter += 1

    if $counter > 5

        sum = 0

        #line 43
        for i in 1..5 do
            # this one is line 45
            sum += $averageArr[$averageArr.count - i]

        end


        return sum/5
        $currAve = sum/5

    else

        return 'WAITING FOR QUOTE. CURRENT:'

    end
end


# line 62
for i in 1..10 do

    # line 64
    getAverage(stock, venue, account)

    if $counter > 5

        if getQuote(stock, venue, account) < $currAve - 25 and numShares < 999

            order = {

                    "account" => account,
                    "venue" => venue,
                    "symbol" => stock,
                    "price" => 1,  #$250.00 -- probably ludicrously high
                    "qty" => 1,
                    "direction" => "buy",
                    "orderType" => "market"  # See the order docs for what a limit order is

                  }

            response = HTTParty.post("#{base_url}/venues/#{venue}/stocks/#{stock}/orders",
                                   :body => JSON.dump(order),
                                   :headers => {"X-Starfighter-Authorization" => apikey}
                                   )

        elsif getQuote(stock, venue, account) > $currAve + 25 and numShares > 0

            order = {

                    "account" => account,
                    "venue" => venue,
                    "symbol" => stock,
                    "price" => 1,  #$250.00 -- probably ludicrously high
                    "qty" => 1,
                    "direction" => "sell",
                    "orderType" => "market"  # See the order docs for what a limit order is

                  }

            response = HTTParty.post("#{base_url}/venues/#{venue}/stocks/#{stock}/orders",
                                   :body => JSON.dump(order),
                                   :headers => {"X-Starfighter-Authorization" => apikey}
                                   )

        end
    end
end

I've been having difficulty with line 45 (commented), in which I get errors about FixNum and nil:

/Users/kaichristensen/Dropbox/Kai/Stockfighter/level_three_selling.rb:45:in `+': nil can't be coerced into Fixnum (TypeError)
from /Users/kaichristensen/Dropbox/Kai/Stockfighter/level_three_selling.rb:45:in `block in getAverage'
from /Users/kaichristensen/Dropbox/Kai/Stockfighter/level_three_selling.rb:43:in `each'
from /Users/kaichristensen/Dropbox/Kai/Stockfighter/level_three_selling.rb:43:in `getAverage'
from /Users/kaichristensen/Dropbox/Kai/Stockfighter/level_three_selling.rb:64:in `block in <main>'
from /Users/kaichristensen/Dropbox/Kai/Stockfighter/level_three_selling.rb:62:in `each'
from /Users/kaichristensen/Dropbox/Kai/Stockfighter/level_three_selling.rb:62:in `<main>'

I might be trying to access and index out of scope on the array, but that doesn't seem to be the problem. Any help would be appreciated.

Answer 1

Your syntax is fine. The problem is that your methods are not validating data.

a += b expands to a = a + b, which will throw the error you're facing when b is nil.

You need to make sure that getQuote always returns a number, or cast whatever you want to average into a number before performing mathematical operations.

For the former, you can change return orderbook["last"] to return orderbook["last"].to_f

For the latter, sum += $averageArr[$averageArr.count - i].to_f