1. Histogram vs. Bar chart

　　 With bar charts, each column represents a group defined by a categorical variable; and with histograms, each column represents a group defined by a quantitative variable.Which means we can change the order of categories in bar chart. But we can not swap the quantitative variable in histogram.

2.We can use map() combined with dictionary/Series to convert our target data to the data we want to.

　　series = ["Yes", "No", NaN, "Yes"] #Origonal data set

　　yes_no = {"Yes": True,"No": False} # The dictionary we would like to convert all the Yes to True, and all the No to False

　　series = series.map(yes_no) # use the map function

3.

Data Cleaning 5