在R中保持变量不变的预测边际/预测。

I recently switched to R, and I love it. But one of the things I miss the most is being able to generate predicted model responses holding certain variables at preset levels (the mean, 90th percentile, etc). This comes in enormously handy when trying to discern the effect of interaction terms, transformed variables, etc.I recently switched to R, and I love it. But on