Conditional sums based on conditional drop down selections - excel

Question

My excel sheet looks something like this:
Animal | Weight | Date
Dog 5 Jan/1/2015
Cat 2 Feb/19/2015
Cow 9 Jan/2/2015
Cow 6 Jan/1/2015
Dog 1 Jan/1/2015
Dog 4 Mar/1/2015
I then would like a to have out like this where the first column is a drop down, the second is a dropdown as well and the third is a total:
Choose Animal | Choose Month | Sum of all the weight:
[Dog,Cow,Cat] | [Jan - Dec] | [Sum of the animal chosen for that month]
So I would like to choose an animal, then choose a month and it should sum the weight. For example if I chose Dog and Jan the total weight should equal 6 (5+1). I am unsure how to accomplish this as it needs to take the sum from the first section, but the criteria for that section is based on the dropdown values of the the second section (unsure if I can even create dropdowns such as this?)

Answer 1

You can use 'Data' => 'data validation' => 'list' to create drop down options (e.g. have the list of options on a separate worksheet, and select that as source range)
As for the sum calculation, I'm not entirely sure what you are after - but imagine you could use VLOOKUP with the wildcard to discard all the text after the month, e.g. :
=VLOOKUP(A1&"*",[range],[column no. where weight is],FALSE)
Using that value to then sum in the next cell with something like:
=SUM(A2,IF(ISERROR(VLOOKUP(A1&"*",[Range],2,FALSE)),0,VLOOKUP(A1&"*",[Range],2,FALSE)))
Potential problem questions though are for instance...
Does the year in the date not matter at all?
What were you planning for months where there are multiple weight inputs for the animal? (like for 'cow'/'Jan' in your example, if that occurs in your actual data)
Hope that helps you get started though!