Function add

src/danfojs-node/test/core/frame.test.ts:1592–1594

(x: any)

                const df = new DataFrame(data)

                const add = (x: any) => {
                    return x + 1000
                }
                const expected = [[1000, 1002, 1004], [1360, 1180, 1360], [1000, 1002, 1004]]
                const dfApply = df.applyMap(add) as DataFrame
                assert.deepEqual(dfApply.values, expected)