Comparing Dates Across Multiple Variables - r

Question

I'm attempting to figure out the amount of days in between games and if that has an impact on wins/losses, this is the information I'm starting with:
schedule:
Home
Away
Home_Final
Away_Final
Date
DAL
OAK
30
35
9/1/2015
KC
PHI
21
28
9/2/2015
This is the result I'd like to get:
Home
Away
Home_Final
Away_Final
Date
Home_Rest
Away_Rest
Adv
Adv_Days
Adv_Won
DAL
OAK
30
35
9/1/2015
null
null
null
null
null
KC
PHI
21
28
9/2/2015
null
null
null
null
null
DAL
PHI
28
7
9/9/2015
8
7
1
1
1
OAK
KC
14
21
9/9/2015
8
7
1
1
0
'Home_Rest' = The home teams amount of days between their games
'Away Rest' = The away teams amount of days between their games
'Adv' = True/False that there was an advantage on one side
'Adv_Days' = The amount of advantage in days
'Adv_Won' = The side with the advantage won
Here is what I've tried, I was able to get it to count how many days were between games for one team, but when I bring all the other ones in I can't wrap my head around how to do that.
library(tidyverse)
library(lubridate)
team_post <- schedule %>% filter(home == 'PHI' | visitor == 'PHI')
day_dif = interval(lag(ymd(team_post$date)), ymd(team_post$date))
team_post <- team_post %>% mutate(days_off = time_length(day_dif, "days"))

Answer 1

You can extend this to all teams using a grouped mutate. See docs for group_by() here.
Something like
schedule %>%
group_by(vars_to_group_by) %>%
mutate(new_var = expr_to_calculate_new_var)
In future, it would be helpful if you included code to recreate a minimal dataset for your example.

Answer 2

The problem is that before you can calculate differences between dates, you must put your dataframe in a friendlier format. Because the Date applies to both teams, that is, one item applies to two columns in the dataframe, which makes it difficult to give it a uniform treatment.
We'll add an id (row number) to the schedule dataframe, as a primary key, so it becomes easy to identify the rows later on.
schedule <- tidyr::tribble(
~Home, ~Away, ~Home_Final, ~Away_Final, ~Date,
"DAL", "OAK", 30, 35, "9/1/2015",
"KC", "PHI", 21, 28, "9/2/2015",
"DAL", "PHI", 28, 7, "9/9/2015",
"OAK", "KC", 14, 21, "9/9/2015"
)
schedule <- schedule %>% mutate(id = row_number())
> schedule
# A tibble: 4 x 6
Home Away Home_Final Away_Final Date id
<chr> <chr> <dbl> <dbl> <chr> <int>
1 DAL OAK 30 35 9/1/2015 1
2 KC PHI 21 28 9/2/2015 2
3 DAL PHI 28 7 9/9/2015 3
4 OAK KC 14 21 9/9/2015 4
Now we'll place your dataframe in a more 'relational' format.
schedule_relational <-
rbind(
schedule %>%
transmute(
id,
Team = Home,
Role = "Home",
Final = Home_Final,
Date
),
schedule %>%
transmute(
id,
Team = Away,
Role = "Away",
Final = Away_Final,
Date
)
)
> schedule_relational
# A tibble: 8 x 5
id Team Role Final Date
<int> <chr> <chr> <dbl> <chr>
1 1 DAL Home 30 9/1/2015
2 2 KC Home 21 9/2/2015
3 3 DAL Home 28 9/9/2015
4 4 OAK Home 14 9/9/2015
5 1 OAK Away 35 9/1/2015
6 2 PHI Away 28 9/2/2015
7 3 PHI Away 7 9/9/2015
8 4 KC Away 21 9/9/2015
How about that!
Now it becomes easy to calculate the difference between dates of games for each team:
schedule_relational <-
schedule_relational %>%
group_by(Team) %>%
arrange(Date) %>%
mutate(Rest = mdy(Date) - mdy(lag(Date))) %>%
ungroup()
> schedule_relational
# A tibble: 8 x 6
id Team Role Final Date Rest
<int> <chr> <chr> <dbl> <chr> <drtn>
1 1 DAL Home 30 9/1/2015 NA days
2 1 OAK Away 35 9/1/2015 NA days
3 2 KC Home 21 9/2/2015 NA days
4 2 PHI Away 28 9/2/2015 NA days
5 3 DAL Home 28 9/9/2015 8 days
6 4 OAK Home 14 9/9/2015 8 days
7 3 PHI Away 7 9/9/2015 7 days
8 4 KC Away 21 9/9/2015 7 days
Observe that the appropriate function to convert dates in character format is mdy(), because your dates are in month/day/year format.
We're very close to a solution! Now all we have to do is to pivot your data back to the wider format. We'll join back the data on the home team and away team by using the id as our unique key.
result <-
schedule_relational %>%
pivot_wider(
names_from = Role,
values_from = c(Team, Final, Rest),
names_glue = "{Role}_{.value}"
)
> result
# A tibble: 4 x 8
id Date Home_Team Away_Team Home_Final Away_Final Home_Rest Away_Rest
<int> <chr> <chr> <chr> <dbl> <dbl> <drtn> <drtn>
1 1 9/1/2015 DAL OAK 30 35 NA days NA days
2 2 9/2/2015 KC PHI 21 28 NA days NA days
3 3 9/9/2015 DAL PHI 28 7 8 days 7 days
4 4 9/9/2015 OAK KC 14 21 8 days 7 days
We'll adjust column names and ordering, and make the final calculations now.
result_final <-
result %>%
transmute(
Home = Home_Team,
Away = Away_Team,
Home_Final,
Away_Final,
Date,
Home_Rest,
Away_Rest,
Adv = as.integer(Home_Rest != Away_Rest),
Adv_Days = abs(Home_Rest != Away_Rest),
Adv_Won = as.integer(Home_Rest > Away_Rest & Home_Final > Away_Final | Away_Rest > Home_Rest & Away_Final > Home_Final)
)
> result_final
# A tibble: 4 x 10
Home Away Home_Final Away_Final Date Home_Rest Away_Rest Adv Adv_Days Adv_Won
<chr> <chr> <dbl> <dbl> <chr> <drtn> <drtn> <int> <int> <int>
1 DAL OAK 30 35 9/1/2015 NA days NA days NA NA NA
2 KC PHI 21 28 9/2/2015 NA days NA days NA NA NA
3 DAL PHI 28 7 9/9/2015 8 days 7 days 1 1 1
4 OAK KC 14 21 9/9/2015 8 days 7 days 1 1 0
It would be interesting if instead of reducing Adv and Adv_Won to yes/no (discrete) values, you'd track the number of days of rest and difference in score. Therefore you could correlate the results also in terms of magnitude.
I've made the code step by step, so you can see intermediate results and understand it better. You may later coalesce some of the statements if you want.
There may be more convoluted solutions, but this is very clear to read and understand.