abs(): Series {
    if (['bool', 'string', 'object'].indexOf(this.dtype.dtype) >= 0) return this.copy();

    return new Series(this.values.map(v => Math.abs(v)), {name: this.name, index: this.index});
  }
Return Series with absolute value of all values

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

@returns {Series}

@example
const ds = new Series([-1, 2, -4, 5, -1, -2]);

// Returns Series([1, 2, 4, 5, 1, 2]);
ds.abs();