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The pie chart question seems like a bad idea. We could not find a clear, elegant answer, and it ends exposing the workings of geom_bar in a way that might be unwise.
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cumulative logical operators probably should not be covered so early. They are a bit difficult to explain, relative to how often they are used. In addition, it seems unwise to introduce row order depended operators before arrange.
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Modular arithmetic should be introduced later than it is. It is an important topic in general programming, but it is not a common function in data science.
ceiling,floor,trunc,roundandsignifcan achieve most or all of the same effects, and can be applied to floating point numbers -
Converting timestamps to times is probably a bit involved for this point in the book, unless you want to give a feel for messy data
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Not clear what delay means in chapter 4
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modular arithmetic stuff can probably go