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Find an average sold price of an eBay search.Do a search for a product, check the "Sold listings" option under "Show only" in the left navigation.Run this script by pasting it into the console tab of the chrome developer tools.
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| function Stats(arr) { | |
| var self = this; | |
| var theArray = arr || []; | |
| //http://en.wikipedia.org/wiki/Mean#Arithmetic_mean_.28AM.29 | |
| self.getArithmeticMean = function() { | |
| var sum = 0, length = theArray.length; | |
| for(var i=0;i<length;i++) { | |
| sum += theArray[i]; | |
| } | |
| return sum/length; | |
| } | |
| //http://en.wikipedia.org/wiki/Standard_deviation | |
| self.getStandardDeviation = function() { | |
| var arithmeticMean = this.getArithmeticMean(); | |
| var sum = 0, length = theArray.length; | |
| for(var i=0;i<length;i++) { | |
| sum += Math.pow(theArray[i]-arithmeticMean, 2); | |
| } | |
| return Math.pow(sum/length, 0.5); | |
| } | |
| self.setArray = function(arr) { | |
| theArray = arr; | |
| return self; | |
| } | |
| self.getArray = function() { | |
| return theArray; | |
| } | |
| return self; | |
| } | |
| var listings = {}; | |
| var soldPrices = []; | |
| $('.bidsold').each(function(k,v) | |
| { | |
| if ($(this).find('.sboffer').length > 0) { | |
| return; | |
| } | |
| var listingId = $(v).closest('li').attr('listingid'); | |
| var price = parseFloat($(v).html().trim().replace('$','').replace(',','')); | |
| listings[listingId] = { | |
| 'price': price, | |
| 'total': price | |
| }; | |
| soldPrices.push(price); | |
| }); | |
| //console.log(listings); | |
| //console.log(soldPrices); | |
| var stat = Stats(soldPrices); | |
| var mean = stat.getArithmeticMean().toFixed(2); | |
| var stdDev = stat.getStandardDeviation().toFixed(2); | |
| var message = 'Mean: $' + mean + '\n'; | |
| message += 'Standard Deviation: $' + stdDev + '\n'; | |
| var goodDeal = 0.5; | |
| message += 'Mean minus ' + goodDeal*100 + '% standard deviation (good deal): $' + (mean - (stdDev*goodDeal)).toFixed(2) + '\n'; | |
| message += 'Mean minus one standard deviation (great deal): $' + (mean - stdDev).toFixed(2); | |
| alert(message); |
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