# [R] Calculating date difference in days

Jeff Newmiller jdnewm|| @end|ng |rom dcn@d@v|@@c@@u@
Thu May 23 00:59:39 CEST 2019

```At the point where you say "date difference in days" IMO you have departed from what `difftime` is for and are in the realm of a numeric measure. I ignore the units inside `difftime` at all times and convert to numeric with a units argument if I want to be that specific about how the measure is represented.

You may or may not recall the difference between angle ABC and the measure of angle ABC (with a bar over it) from geometry... but the idea is the same... distinguish the thing (time interval) from the numbers used to quantify it (numeric).

elapsed_days <- function(end_date, start_date){
ed <- as.POSIXlt(end_date)
sd <- as.POSIXlt(start_date)
as.numeric( ed-sd, units="days" )
}

On May 22, 2019 2:43:42 PM PDT, reichmanj using sbcglobal.net wrote:
>R Help
>
>I have a function to calculate a date difference in days but my results
>come
>back in hours.  I suspect I am using the as.POSIXlt function
>incorrectly .
>
>Suggestions?
>
># Start time of data to be considered
>start_day <- "2016-04-30"
>
># Make event and sequence IDs into factors
>elapsed_days <- function(end_date, start_date){
>  ed <- as.POSIXlt(end_date)
>  sd <- as.POSIXlt(start_date)
>  ed-sd
>}
>
>trans_sequence\$eventID <- elapsed_days(trans_sequence\$Date, start_day)
>
>
>> trans_sequence
># A tibble: 39 x 5
># Groups:   Emitter [15]
>   Emitter Date        SIZE Geohash
>eventID
>     <int> <date>     <int> <chr>
><time>
> 1       1 2016-05-01    12 A;B;C;D;E;F;G;H;I;J;K;L
>19 hours
> 2       1 2016-05-02     5 A;B;C;D;E
>43 hours
> 3       1 2016-05-05    11 A;B;C;D;E;F;G;H;I;J;K
>115 hours
> 4       2 2016-05-01     9 C;D;E;F;G;H;I;J;K
>19 hours
> 5       2 2016-05-02     3 F;G;H
>43 hours
> 6       2 2016-05-05     3 L;M;N
>115 hours
> 7       3 2016-05-01     3 L;M;N
>19 hours
> 8       3 2016-05-02     3 I;J;K
>43 hours
> 9       3 2016-05-04    25
>A;B;C;D;E;F;G;H;I;J;K;L;M;N;O;P;Q;R;S;T;U;V;W;X;Y  91 hours
>10       3 2016-05-05     7 O;P;Q;R;S;T;U
>115 hours
>
>Jeff Reichman
>
>
>	[[alternative HTML version deleted]]
>
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