title: Finding averages per month from a list that contains multiple entries for each month
body: <p>I am trying to find the average values for each month by using a function that references a sorted list of tuples containing (date,value) where date is a string and in the format yyyy-mm-dd and value is a float. The first entry in the data set is not showing up and I believe there may be more errors that I am not aware of. This is what I have so far in Python (note, previous functions not included):</p>
  
  <pre><code>def value_avg(previous_tuple_list):
      start_month=tup_list[0][0]
      start_month1=start_month.split("/")
      start_month2=start_month1[1]
      value_total=0
      value_count=0
      value_avglist=[]
  for item in tuple_list:
      value_month=tup[0]
      value_month1=value_month.split("/")
      value_month2=value_month1[1]
      value=item[1]
      if value_month2==start_month2:
          value_sum += value
          value_count += 1
      else:
          value_avg=(value_sum / value_count)
          date_no_day= item[0][:7]
          value_avg_tup=(value_avg, date_no_day)
          value_avglist.append(value_avg_tup)
          value_sum -= value_sum
          value_count -= value_count
          start_month2 = value_month2
  </code></pre>