A method compares data sets in a data preparation application. The method displays a user interface including a data flow pane and a profile pane. The data flow pane displays a flow diagram with nodes, each node corresponding to a data set. When a user selects a first node, the method displays distributions of data values for data fields from a first data set for the first node. When a user selects a second node, the method: (1) forms a composite data set comprising a union of (i) the first data set and (ii) a second data set for the second node; (2) groups data values for each data field to form sets of bins; and (3) displays data value distributions for each data field using the bins. Each bin depicts counts of data values in the bin originating from the first data set and the second data set.