corrFunc = function corrFunc(ds1, ds2) {
        // $FlowFixMe TODO
        return ds1.values === ds2.values ? 1 : ds1.corr(ds2);
      }
Calculate the correlation between all `Series` in the `DataFrame`

pandas equivalent: [DataFrame.corr](http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.corr.html)

@return {DataFrame}

@example
const df = new DataFrame([{x: 1, y: 2, z: 3}, {x: 2, y: 1, z: 5}, {x: 3, y: 0, z: 7}]);

// Returns DataFrame([{x: 1, y: -1, z: 1}, {x: -1, y: 1, z: -1}, {x: 1, y: -1, z: 1}])
df.corr();