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  • Jeff Boltz thinks this is interesting:

tipsCoef <- within(tipsCoef, {
+     Lower <- Estimate - qt(p=0.90, df=tipsInfo$df[2]) * `Std...

From

Cover of R for Everyone: Advanced Analytics and Graphics, 2nd Edition

Note

Got error

Error in +(day <- rownames(tipsCoef)) : invalid argument to unary operator