Well, that was a short lived coup. On the back of Monster Hunter World, the PS4 had been outselling the Switch (which had otherwise steadfastly been the highest selling system in Japan every week for most of the weeks since its launch) for the last few weeks; that has reverted back to how things used to be, however.
The newest round of Media Create numbers are out, and they show the Switch outselling the PS4 handily. The Switch sold almost 40,000 units, while the PS4 was at almost 35,000 units. The Switch managed this in spite of no new releases, versus the PS4, which got quite a few new games that all ended up charting on the software charts.
That said, the top of the chart was still reserved for Monster Hunter World, which continues its historic reign atop the software charts in the country; elsewhere, Switch evergreen games such as Breath of the Wild, Super Mario Odyssey, Splatoon 2, and Mario Kart 8 Deluxe all continued to have strong showings as well.