def std(self, sample=False):
        """Returns the standard deviation of the values in this expression,
        which must resolve to a numeric array.

        Missing or ``None``-valued elements are ignored.

        By default, the population standard deviation is returned. If you wish
        to compute the sample standard deviation instead, set ``sample=True``.

        See https://en.wikipedia.org/wiki/Standard_deviation#Estimation for
        more information on population (biased) vs sample (unbiased) standard
        deviation.

        Examples::

            import fiftyone as fo
            import fiftyone.zoo as foz
            from fiftyone import ViewField as F

            dataset = foz.load_zoo_dataset("quickstart")

            # Add a field to each `predictions` object that records the
            # standard deviation of the confidences
            view = dataset.set_field(
                "predictions.conf_std",
                F("detections").map(F("confidence")).std()
            )

            print(view.bounds("predictions.conf_std"))

        Args:
            sample (False): whether to compute the sample standard deviation
                rather than the population standard deviation

        Returns:
            a :class:`ViewExpression`
        """
        if sample:
            return ViewExpression({"$stdDevSamp": self})

        return ViewExpression({"$stdDevPop": self})
Returns the standard deviation of the values in this expression,
        which must resolve to a numeric array.

        Missing or ``None``-valued elements are ignored.

        By default, the population standard deviation is returned. If you wish
        to compute the sample standard deviation instead, set ``sample=True``.

        See https://en.wikipedia.org/wiki/Standard_deviation#Estimation for
        more information on population (biased) vs sample (unbiased) standard
        deviation.

        Examples::

            import fiftyone as fo
            import fiftyone.zoo as foz
            from fiftyone import ViewField as F

            dataset = foz.load_zoo_dataset("quickstart")

            # Add a field to each `predictions` object that records the
            # standard deviation of the confidences
            view = dataset.set_field(
                "predictions.conf_std",
                F("detections").map(F("confidence")).std()
            )

            print(view.bounds("predictions.conf_std"))

        Args:
            sample (False): whether to compute the sample standard deviation
                rather than the population standard deviation

        Returns:
            a :class:`ViewExpression`
        
fiftyone/core/expressions.py