def reduce_metrics(logging_outputs) -> None:
        """Aggregate logging outputs from data parallel training."""

        loss_sum = utils.item(sum(log.get("loss", 0) for log in logging_outputs))
        ntokens = utils.item(sum(log.get("ntokens", 0) for log in logging_outputs))
        nsentences = utils.item(
            sum(log.get("nsentences", 0) for log in logging_outputs)
        )
        sample_size = utils.item(
            sum(log.get("sample_size", 0) for log in logging_outputs)
        )

        metrics.log_scalar(
            "loss", loss_sum / sample_size / math.log(2), sample_size, round=3
        )
        metrics.log_scalar("ntokens", ntokens)
        metrics.log_scalar("nsentences", nsentences)
        if sample_size != ntokens:
            metrics.log_scalar(
                "nll_loss", loss_sum / ntokens / math.log(2), ntokens, round=3
            )

        c_errors = sum(log.get("c_errors", 0) for log in logging_outputs)
        metrics.log_scalar("_c_errors", c_errors)
        c_total = sum(log.get("c_total", 0) for log in logging_outputs)
        metrics.log_scalar("_c_total", c_total)
        w_errors = sum(log.get("w_errors", 0) for log in logging_outputs)
        metrics.log_scalar("_w_errors", w_errors)
        wv_errors = sum(log.get("wv_errors", 0) for log in logging_outputs)
        metrics.log_scalar("_wv_errors", wv_errors)
        w_total = sum(log.get("w_total", 0) for log in logging_outputs)
        metrics.log_scalar("_w_total", w_total)

        if c_total > 0:
            metrics.log_derived(
                "uer",
                lambda meters: safe_round(
                    meters["_c_errors"].sum * 100.0 / meters["_c_total"].sum, 3
                )
                if meters["_c_total"].sum > 0
                else float("nan"),
            )
        if w_total > 0:
            metrics.log_derived(
                "wer",
                lambda meters: safe_round(
                    meters["_w_errors"].sum * 100.0 / meters["_w_total"].sum, 3
                )
                if meters["_w_total"].sum > 0
                else float("nan"),
            )
            metrics.log_derived(
                "raw_wer",
                lambda meters: safe_round(
                    meters["_wv_errors"].sum * 100.0 / meters["_w_total"].sum, 3
                )
                if meters["_w_total"].sum > 0
                else float("nan"),
            )
Aggregate logging outputs from data parallel training.
understand_icl/fairseq/fairseq/criterions/ctc.py