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  1. #1
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    Exclamation How do you make an automatic price averager? (Read)

    I'm having a bit of an issue, in the real world there's an economy of goods and prices, an ever changing one, The average price on a jar of honey may be $3 today but in 4 days it could be $3.25, everything changes constantly, is there a way where i could do something like this with tables? I want to be able to let users put in what the think a good price for the item would be and it takes the other prices and averages them automatically and displays the price. For example,

    I have listed an apple, the starting value of the apple is $3
    User 1 thinks the apple is worth around $4
    ($4 + $3)x .5 = $3.50 (Average cost of an Apple)
    This price is now displayed to the community, that the average price of an apple is $3.50, now say another user comes around,
    User 2 thinks the apple is somewhere around $2.75
    ($4 + $3 + $2.75) x .5 = $4.87
    Now, the average price of an apple that would be displayed to the community is $4.87, is there something like this that i could use on my website? Whether it is open source or not doesn't matter, something that will check the MySQL databases for previous data and average out the information/prices/data to give an end average price between the submitted prices?

    I've been having quite some trouble with this issue, i'm looking to create a price guide for online items in a gaming community, is there an easy way to do this?

  • #2
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    Because you don't know how many items there will be, or how many values
    are placed on those items, I would think you would have one table in your MySQL
    database that stores all of them. Each time someone gives a value to an apple,
    it would insert a new line. There could be 50 rows for apples, 30 rows for oranges,
    and 100 rows for bananas. You query for a particular item, you know how many
    rows it found, and you SUM the values ... now you can determine the average.

    If you also add a column with a timestamp, you could query the table for an item
    within a certain amount of time (days, months, years). You may want to know the
    average price for the apples only during the past month.

    That's my take on it anyhow.


    .

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    skill3d (02-24-2012)

  • #3
    Regular Coder Lerura's Avatar
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    in your example that average goes up after the third entry even if the new entry was lower than the previous average.

    You can't just divide the sum by 2 each time a new entry has come in.
    Then if the next 97 entries all are $3.50 then you would have average of

    (4 + 3 + 2 + 97x3.50)*.5 = 174,63.

    You only need to store the number of entries along with the count of entries.

    After the first 2 entries .
    you will have

    EntrySum = 7;
    EntryCount = 2;

    And then for each new entry:

    EntrySum += NewEntry;
    EntryCount++;

    After the 3 third it would be:

    EntrySum = 9.75;
    EntryCount = 3;

    And then the average would be EntrySum(9.75) / EntryCount(3) = 3.25.

    You could for the statistics also store the highest and the lowest entry.

    And use:
    EntryMax = Max(EntryMax, NewEntry)
    EntryMin = Min(EntryMin, NewEntry)
    to set the new value

    But if you also want to know the what entry was entered most times, then you will need to store each and every entry seperately.

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    skill3d (02-24-2012)

  • #4
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    Thank you both very much, hopefully with your replies and some other information on coding this, i'll be able to get it done with-in the next couple days. Your information was very useful. Thanked, -Skill3d


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