const dfd = require("danfojs-node")
let data ={A: ['foo', 'bar', 'foo', 'bar',
'foo', 'bar', 'foo', 'foo'],
B: ['one', 'one', 'two', 'three',
'two', 'two', 'one', 'three'],
let df = new dfd.DataFrame(data)
let grp = df.groupby(["A","B"])
grp.col(["C","D"]).std().print()