In base GFLOPS terms, the Switch is 157 GFLOPS undocked and 393 GFLOPS docked, when we assume Eurogamer's clocks are correct. There are other things, that are hard to quantify exactly, that improve the Switch relative to the PS4 and Xbox One, namely architecture (the Switch architecture is likely a bit more efficient for every FLOP it has) and a technique called half-precision computation, which has the potential to add quite a significant percentage. According to one very technically proficient GAFfer (Thraktor), this half-precision should be easily implementable, and one dev on GAF said that a gain of 54% could be had from this technique (though I am very sceptical that this will be achievable in every game, it just sounds too big not to have been used much earlier in console tech).
Anyway, you can assume the Switch is 1-1.5 times as powerful as the WiiU in undocked mode, and about 1/3 to 50% of Xbox One when disregarding the aforementioned half-precision calculations.