Tidyr's gather() with NAs

问题

I am using tidyr and lubridate to convert a wide table to a long table. The following works just fine.

> (df <- data.frame(hh_id = 1:2,
                   bday_01 = ymd(20150309),
                   bday_02 = ymd(19850911),
                   bday_03 = ymd(19801231)))

  hh_id    bday_01    bday_02    bday_03
1     1 2015-03-09 1985-09-11 1980-12-31
2     2 2015-03-09 1985-09-11 1980-12-31

> gather(df, person_num, bday, starts_with("bday_0"))

  hh_id  person_num        bday
1     1     bday_01  2015-03-09
2     2     bday_01  2015-03-09
3     1     bday_02  1985-09-11
4     2     bday_02  1985-09-11
5     1     bday_03  1980-12-31
6     2     bday_03  1980-12-31

However, when there are NA's in the mix, the dates are converted to strings.

> (df <- data.frame(hh_id = 1:2,
                   bday_01 = ymd(20150309),
                   bday_02 = ymd(19850911),
                   bday_03 = NA))

  hh_id    bday_01    bday_02    bday_03
1     1 2015-03-09 1985-09-11         NA
2     2 2015-03-09 1985-09-11         NA

> gather(df, person_num, bday, starts_with("bday_0"))

  hh_id person_num       bday
1     1    bday_01 1425859200
2     2    bday_01 1425859200
3     1    bday_02  495244800
4     2    bday_02  495244800
5     1    bday_03         NA
6     2    bday_03         NA
Warning message:
attributes are not identical across measure variables; they will be dropped

Note that there is still a warning when regular strings are mixed with NA's as well.

> (df <- data.frame(hh_id = 1:2,
                    bday_01 = '20150309',
                    bday_02 = '19850911',
                    bday_03 = NA))

  hh_id  bday_01  bday_02 bday_03
1     1 20150309 19850911      NA
2     2 20150309 19850911      NA

> gather(df, person_num, bday, starts_with("bday_0"))

  hh_id person_num     bday
1     1    bday_01 20150309
2     2    bday_01 20150309
3     1    bday_02 19850911
4     2    bday_02 19850911
5     1    bday_03     <NA>
6     2    bday_03     <NA>
Warning message:
attributes are not identical across measure variables; they will be dropped

Is it possible to use tidyr with NA's while avoiding a warning and retaining formatting?

回答1:

The data is not being converted to strings, it is dropping back to the integer representation of the seconds since 1970-01-01, which is what the original Date values in df represent:

x <- df$bday_01
x
#[1] "2015-03-09 UTC" "2015-03-09 UTC"
attributes(x) <- NULL
x
#[1] 1425859200 1425859200

The warning message gives you a hint to a way around it:

attributes are not identical across measure variables; they will be dropped

So, try:

attributes(df$bday_03) <- attributes(df$bday_02)
gather(df, person_num, bday, starts_with("bday_0"))

#  hh_id person_num       bday
#1     1    bday_01 2015-03-09
#2     2    bday_01 2015-03-09
#3     1    bday_02 1985-09-11
#4     2    bday_02 1985-09-11
#5     1    bday_03       <NA>
#6     2    bday_03       <NA>

来源：https://stackoverflow.com/questions/28954585/tidyrs-gather-with-nas

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lubridate

tidyr