reduced code

    ch_samtools_bam

        .map { row ->

            def denominator = row[0].find{ it.key == "bt2_total_aligned_spikein" }?.value.toInteger()

            denominator = (denominator != 0 ? denominator : 1)

            [ row[0].id, params.normalisation_c / denominator ]

            [ row[0].id, params.normalisation_c / (denominator != 0 ? denominator : 1) ]

        }

        .set { ch_scale_factor }

    // EXAMPLE CHANNEL STRUCT: [id, scale_factor]