calculating number of days between 2 columns of dates in data frame

Question

I have a data frame which has two columns of dates in the format yyyy mm dd  I am trying to calculate the number of days between these two dates for each observation within the data frame  and create a new variable with this number of days in it   So far I have tried using the answer given here  Calculate the number of weekdays between 2 dates in R but editing the code so that it calculates number of total days rather than just the number of week days  This just came up with error saying  Error in del by   non-numeric argument to binary operator In addition  Warning message  In Ops factor to  from    - not meaningful for factors  I have also attempted using this code  finish  lt - as Date survey date  format  quot  yyyy  mm  dd quot   start  lt - as Date survey tx start  format  quot  yyyy  mm  dd quot   date diff lt -as data frame finish-start   with the plan of using  quot cbind quot  or something equivalent to combine the data frame  quot days quot  to my data frame  quot survey quot  which has data in it  Although this does not give me any errors  the observations within the  quot finish quot  and  quot start quot  objects are all  quot NA real  quot   and the date diff data frame therefore has all the observations listed as NA  If someone could point me in the right direction that would be great  All the other question I have found do not seem to be dealing with dates within variables but as individual dates  and applying those techniques to variables hasn t been working for me

User · Answer

You could find the difference between dates in columns in a data frame by using the function difftime as follows   df diff in days lt - difftime df datevar1  df datevar2   units   c  days

User · Answer

In Ronald s example  if the date formats are different  as displayed below  then modify the format parameter  survey  lt - data frame date c  2012-07-26   2012-07-25   tx start c  2012-01-01   2012-01-01     survey date diff  lt - as Date as character survey date   format   Y- m- d  -               as Date as character survey tx start   format   Y- m- d     survey      date      tx start     date diff 1 2012-07-26     2012-01-01    207 days 2 2012-07-25     2012-01-01    206 days

User · Answer

Without your seeing your data  you can use the output of dput head survey   to show us  this is a shot in the dark   survey  lt - data frame date c  2012 07 26   2012 07 25   tx start c  2012 01 01   2012 01 01     survey date diff  lt - as Date as character survey date   format   Y  m  d  -                   as Date as character survey tx start   format   Y  m  d   survey        date   tx start date diff 1 2012 07 26 2012 01 01  207 days 2 2012 07 25 2012 01 01  206 days

User · Answer

You need to use the as Date formats correctly   Eg   x    2012 07 25  xd   as Date x   Y  m  d   xd      Prints  2012-07-25    R date formats are similary to  nix ones   Doing a  typeof xd  shows it as a double ie  days since 1970

User · Answer

Following Ronald Example I would like to add that it should be considered if the origin and end dates must be included or not in the days count between two dates  I faced the same problem and ended up using a third option with apply  It could be memory inefficient but helps to understand the problem      survey  lt - data frame date c  2012 07 26   2012 07 25   tx start c  2012 01 01   2012 01 01     survey diff 1  lt - as numeric    as Date as character survey date   format   Y  m  d  -     as Date as character survey tx start   format   Y  m  d      survey diff 2 lt - as numeric    difftime survey date  survey tx start   units   c  days       survey diff 3  lt - apply X   survey  c  date    tx start                            MARGIN   1                         FUN   function x                           length                             seq Date                               from   as Date x 2                                 to   as Date x 1                                 by    day                                                           This gives the following date differences           date   tx start diff 1   diff 2 diff 3 1 2012 07 26 2012 01 01    207 206 9583    208 2 2012 07 25 2012 01 01    206 205 9583    207

[r] calculating number of days between 2 columns of dates in data frame

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