you add these up for each individual class for exampleif the proportion of the datathat isfor given class is then the contribution to the overall entropy is and if everything is that classthen again the contribution to the overall entropy is because in either caseif nothing is this class or everything is this classthat' not really contributing anything to the overall entropy it' the things in the middle that contribute entropy of the classwhere there' some mixture of this classification and other stuff when you add all these terms togetheryou end up with an overall entropy for the entire dataset so mathematicallythat' how it works outbut againthe concept is very simple it' just measure of how disordered your datasethow same or different the things in your data are decision trees concepts believe it or notgiven set of training datayou can actually get python to generate flowchart for you to make decision so if you have something you're trying to predict on some classificationyou can use decision tree to actually look at multiple attributes that you can decide upon at each level in the flowchart you can print out an actual flowchart for you to use to make decision frombased on actual machine learning how cool is thatlet' see how it works personally find decision trees are one of the most interesting applications of machine learning decision tree basically gives you flowchart of how to make some decision you have some dependent variablelike whether or not should go play outside today or not based on the weather when you have decision like that that depends on multiple attributes or multiple variablesa decision tree could be good choice there are many different aspects of the weather that might influence my decision of whether should go outside and play it might have to do with the humiditythe temperaturewhether it' sunny or notfor example decision tree can look at all these different attributes of the weatheror anything elseand decide what are the thresholdswhat are the decisions need to make on each one of those attributes before arrive at decision of whether or not should go play outsidethat' all decision tree is so it' form of supervised learning