Page 49 Homework Answers

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  library(tidyverse)
  library(nycflights13)

Problem 1:

  table(filter(flights, month >= 7,  month <= 9)[,"month"])

month
    7     8     9 
29425 29327 27574 

  table(filter(flights, month %in% 7:9)[,"month"])

month
    7     8     9 
29425 29327 27574 

  table(flights[flights$month %in% 7:9, "month"])

month
    7     8     9 
29425 29327 27574 

  
  (dts <- c("2019/02/24 24:00:00", "2019/02/25 00:00:00",
            "2019/02/25 00:00:00.01", "2019/02/24 23:59:59.999999"))

[1] "2019/02/24 24:00:00"        "2019/02/25 00:00:00"       
[3] "2019/02/25 00:00:00.01"     "2019/02/24 23:59:59.999999"

  (dts.posixct <- as.POSIXct(dts))

[1] "2019-02-25 00:00:00 PST" "2019-02-25 00:00:00 PST" "2019-02-25 00:00:00 PST"
[4] "2019-02-24 23:59:59 PST"

  dts.posixct[1] == dts.posixct[2]

[1] TRUE

  dts.posixct[2] - dts.posixct[1]

Time difference of 0 secs

  dts.posixct[3] - dts.posixct[1]

Time difference of 0.00999999 secs

  dts.posixct[3] - dts.posixct[2]

Time difference of 0.00999999 secs

  dts.posixct[2] - dts.posixct[4]

Time difference of 9.536743e-07 secs

Means

  mean(c("a","b","c","d"))

Warning: argument is not numeric or logical: returning NA

[1] NA

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