Given a series of dates and a birth day, is there a way to obtain the age at every date entry along with a final age using the lubridate package?

Question

I have a database of information pertaining to individuals observed over time. I would like to find a way to obtain the age of these individuals whenever a record was taken. Assuming the BIRTH assigns a value of 0, I would like to obtain the age either in days or months for the visits after. It would also be helpful to obtain a final age (either day or month) for each individual (*not included in the code). For example, for ID (A), the final age would be 10 months. I would like to use the lubridate function as it's in-built date feature makes it easier to work with dates. Any help with this is much appreciated.

date<-c("2000-01-01","2000-01-14","2000-01-25","2000-02-12","2000-02-27","2000-06-05","2000-10-30",
        "2001-02-04","2001-06-15","2001-12-26","2002-05-22","2002-06-04",
        "2000-01-08","2000-07-11","2000-08-18","2000-11-27")
ID<-c("A","A","A","A","A","A","A",
      "B","B","B","B","B",
      "C","C","C","C")
status<-c("BIRTH","ETC","ETC","ETC","ETC","ETC","ETC",
          "BIRTH","ETC","ETC","ETC","ETC",
          "BIRTH","ETC","ETC","ETC")

df1<-data.frame(date,ID,status)
print(df1)
         date ID status
1  2000-01-01  A  BIRTH
2  2000-01-14  A    ETC
3  2000-01-25  A    ETC
4  2000-02-12  A    ETC
5  2000-02-27  A    ETC
6  2000-06-05  A    ETC
7  2000-10-30  A    ETC
8  2001-02-04  B  BIRTH
9  2001-06-15  B    ETC
10 2001-12-26  B    ETC
11 2002-05-22  B    ETC
12 2002-06-04  B    ETC
13 2000-01-08  C  BIRTH
14 2000-07-11  C    ETC
15 2000-08-18  C    ETC
16 2000-11-27  C    ETC

date.new<-c("2000-01-01","2000-01-14","2000-01-25","2000-02-12","2000-02-27","2000-06-05","2000-10-30",
        "2001-02-04","2001-06-15","2001-12-26","2002-05-22","2001-02-04",
        "2000-01-08","2000-07-11","2000-08-18","2000-11-27")
ID.new<-c("A","A","A","A","A","A","A",
      "B","B","B","B","B",
      "C","C","C","C")
status.new<-c("BIRTH","ETC","ETC","ETC","ETC","ETC","ETC",
          "BIRTH","ETC","ETC","ETC","ETC",
          "BIRTH","ETC","ETC","ETC")

age<-c(0,1,1,2,2,6,10,
       0,4,10,15,16,
       0,6,7,10)

df2<-data.frame(date.new,ID.new,status.new,age)

print(df2)
     date.new ID.new status.new age
1  2000-01-01      A      BIRTH   0
2  2000-01-14      A        ETC   1
3  2000-01-25      A        ETC   1
4  2000-02-12      A        ETC   2
5  2000-02-27      A        ETC   2
6  2000-06-05      A        ETC   6
7  2000-10-30      A        ETC  10
8  2001-02-04      B      BIRTH   0
9  2001-06-15      B        ETC   4
10 2001-12-26      B        ETC  10
11 2002-05-22      B        ETC  15
12 2001-02-04      B        ETC  16
13 2000-01-08      C      BIRTH   0
14 2000-07-11      C        ETC   6
15 2000-08-18      C        ETC   7
16 2000-11-27      C        ETC  10

Why is the age for `ID` A on `2000-01-14` 1 and not 0? – Bas Mar 31 '22 at 11:11 — Bas, Mar 31 '22 at 11:11
My mistake, should have put 0 instead. – Ananth Jason Apr 11 '22 at 11:13 — Ananth Jason, Apr 11 '22 at 11:13

score 1 · Answer 1 · answered Apr 01 '22 at 14:00

For calculations related to age in years or months, I'd like to encourage you to try the clock package rather than lubridate. lubridate is a great package, but produces some unexpected results with these kinds of calculations if you aren't 100% sure of what you are doing. In clock, the function to do this is date_count_between(). Notice that one of the results is different between clock and lubridate here:

library(clock)
library(lubridate, warn.conflicts = FALSE)
library(dplyr, warn.conflicts = FALSE)

df <- tibble(
  date = c("2000-01-01","2000-01-14",
           "2000-01-25","2000-02-12","2000-02-27","2000-06-05",
           "2000-10-30","2001-02-04","2001-06-15","2001-12-26",
           "2002-05-22","2002-06-04","2000-01-08","2000-07-11",
           "2000-08-18","2000-11-27"),
  ID = c("A","A","A","A","A","A",
         "A","B","B","B","B","B","C","C","C","C"),
  status = c("BIRTH","ETC","ETC","ETC",
             "ETC","ETC","ETC","BIRTH","ETC","ETC","ETC","ETC",
             "BIRTH","ETC","ETC","ETC")
)

df %>% 
  mutate(date = date_parse(date)) %>% 
  group_by(ID) %>% 
  mutate(birth_date = date[status == "BIRTH"]) %>% 
  ungroup() %>%
  mutate(
    age_clock = date_count_between(birth_date, date, "month"),
    age_lubridate = as.period(date - birth_date) %/% months(1))
#> # A tibble: 16 × 6
#>    date       ID    status birth_date age_clock age_lubridate
#>    <date>     <chr> <chr>  <date>         <int>         <dbl>
#>  1 2000-01-01 A     BIRTH  2000-01-01         0             0
#>  2 2000-01-14 A     ETC    2000-01-01         0             0
#>  3 2000-01-25 A     ETC    2000-01-01         0             0
#>  4 2000-02-12 A     ETC    2000-01-01         1             1
#>  5 2000-02-27 A     ETC    2000-01-01         1             1
#>  6 2000-06-05 A     ETC    2000-01-01         5             5
#>  7 2000-10-30 A     ETC    2000-01-01         9             9
#>  8 2001-02-04 B     BIRTH  2001-02-04         0             0
#>  9 2001-06-15 B     ETC    2001-02-04         4             4
#> 10 2001-12-26 B     ETC    2001-02-04        10            10
#> 11 2002-05-22 B     ETC    2001-02-04        15            15
#> 12 2002-06-04 B     ETC    2001-02-04        16            15
#> 13 2000-01-08 C     BIRTH  2000-01-08         0             0
#> 14 2000-07-11 C     ETC    2000-01-08         6             6
#> 15 2000-08-18 C     ETC    2000-01-08         7             7
#> 16 2000-11-27 C     ETC    2000-01-08        10            10

clock says that 2001-02-04 to 2002-06-04 is 16 months, while the lubridate method here only says it is 15 months. This has to do with the fact that the lubridate calculation uses the length of an average month, which doesn't always accurately reflect how we think about months.

Consider this simple example, I think most people would agree that a child born on this date in February is considered "1 month and 1 day" old. But lubridate shows 0 months!

library(clock)
library(lubridate, warn.conflicts = FALSE)

# "1 month and 1 day apart"
feb <- as.Date("2020-02-28")
mar <- as.Date("2020-03-29")

# As expected when thinking about age in months
date_count_between(feb, mar, "month")
#> [1] 1

# Not expected
as.period(mar - feb) %/% months(1)
#> [1] 0

secs_in_day <- 86400
secs_in_month <- as.numeric(months(1))
secs_in_month / secs_in_day
#> [1] 30.4375

# Less than 30.4375 days, so not 1 month
mar - feb
#> Time difference of 30 days

The issue is that lubridate uses the length of an average month in the computation, which is 30.4375 days. But there are only 30 days between these two dates, so it isn't considered a full month.

clock, on the other hand, uses the day component of the starting date to determine if a "full month" has passed or not. In other words, because we have passed the 28th of March, clock decides that 1 month has passed, which is consistent with how we generally think about age.

Today I learned about clock. Thank you – Bas Apr 12 '22 at 08:40 — Bas, Apr 12 '22 at 08:40

score 0 · Answer 2 · answered Mar 31 '22 at 11:18

Using dplyr and lubridate, we can do the following. We first turn the date column into a date. Then we group by ID, find the birth date and calculate the number of months since that date via some lubridate magic (see How do I use the lubridate package to calculate the number of months between two date vectors where one of the vectors has NA values?).

library(dplyr)
library(lubridate)

df1 %>% 
  mutate(date = as_date(date)) %>% 
  group_by(ID) %>% 
  mutate(birth_date = date[status == "BIRTH"],
         age = as.period(date - birth_date) %/% months(1)) %>% 
  ungroup()

Which gives:

   date       ID    status birth_date   age
   <date>     <fct> <fct>  <date>     <dbl>
 1 2000-01-01 A     BIRTH  2000-01-01     0
 2 2000-01-14 A     ETC    2000-01-01     0
 3 2000-01-25 A     ETC    2000-01-01     0
 4 2000-02-12 A     ETC    2000-01-01     1
 5 2000-02-27 A     ETC    2000-01-01     1
 6 2000-06-05 A     ETC    2000-01-01     5
 7 2000-10-30 A     ETC    2000-01-01     9
 8 2001-02-04 B     BIRTH  2001-02-04     0
 9 2001-06-15 B     ETC    2001-02-04     4
10 2001-12-26 B     ETC    2001-02-04    10
11 2002-05-22 B     ETC    2001-02-04    15
12 2002-06-04 B     ETC    2001-02-04    15
13 2000-01-08 C     BIRTH  2000-01-08     0
14 2000-07-11 C     ETC    2000-01-08     6
15 2000-08-18 C     ETC    2000-01-08     7
16 2000-11-27 C     ETC    2000-01-08    10

Which is your expected output except for some rounding differences. See my comment on your question.

Thank you very much, Bas. This has been very helpful – Ananth Jason Apr 11 '22 at 11:12 — Ananth Jason, Apr 11 '22 at 11:12

Given a series of dates and a birth day, is there a way to obtain the age at every date entry along with a final age using the lubridate package?

2 Answers2