Calculate the difference between two weekdays in multiple combinations by name(start/end)-CodePudding

This question is part of this question R - Reclassifying days in relation to another variable

The core and most important part for me is this:

Suppose we have to columns with day names:

df <- structure(list(StartDay = c("Friday", "Friday", "Friday", "Thursday", 
"Friday", "Friday"), NextDay = c("Wednesday", "Tuesday", "Thursday", 
"Wednesday", "Wednesday", "Friday")), class = "data.frame", row.names = c("1", 
"2", "3", "4", "5", "6"))

  StartDay   NextDay
1   Friday Wednesday
2   Friday   Tuesday
3   Friday  Thursday
4 Thursday Wednesday
5   Friday Wednesday
6   Friday    Friday

Is it possible to calculate the difference of these two weekdays where the StartDay is always the starting day:

Desired ouptut:

  StartDay   NextDay difference
1   Friday Wednesday          5
2   Friday   Tuesday          4
3   Friday  Thursday          6
4 Thursday Wednesday          6
5   Friday Wednesday          5
6   Friday    Friday          0

The idea is that StartDay is 0, the next day is 1, the day after is 2, ...

CodePudding user response：

Use match to convert to numbers and then difference them and take that modulo 7.

wdays <- c("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", 
  "Friday", Saturday")
transform(df, diff = apply(apply(df, 2, match, wdays), 1, diff) %% 7)

giving:

  StartDay   NextDay diff
1   Friday Wednesday    5
2   Friday   Tuesday    4
3   Friday  Thursday    6
4 Thursday Wednesday    6
5   Friday Wednesday    5
6   Friday    Friday    0

It could also be expressed as:

transform(df, diff = (match(NextDay, wdays) - match(StartDay, wdays)) %% 7)