[R] Converting time format

[Parkhurst, David]

I have a dataframe obtained using read.csv from an excel file.  Its first column is times, running from 18:00 to 19:30.  If I want to plot other columns against time, do I need to convert those somehow, and how would I do that?

If I run plot(b$time,b$myvar) I get a decent plot, but a friend suggests that R is just treating those numbers as text, and putting them in alphabetical order.  True?

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