Division ?

It seems division with numbers bigger than 10 000 000 doesn't work
 20000000/21
[1] 952381

55555555/23

[1] 2415459

Thank you

I think you are confusing what is displayed with what is computed:

  20000000/21
# [1] 952381
  print(20000000/21,17)
# [1] 952380.9523809524

  55555555/23
# [1] 2415459
  print(55555555/23,17)
# [1] 2415458.913043478

  (20000000/21)*21
# [1] 2e+07
  print((20000000/21)*21,17)
# [1] 2e+07

  (55555555/23)*23
# [1] 55555555
  print((55555555/23)*23,17)
# [1] 55555555

Your "numbers bigger than 10 000 000" corresponds to the default
display of results to 7 significant figures.

If (as in the above print() statements) you increase this, you
get more "reasonable"-looking results.

Hoping this helps,
Ted.

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E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
Fax-to-email: +44 (0)870 094 0861
Date: 03-May-09                                       Time: 10:11:02
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It seems division with numbers bigger than 10 000 000 doesn't work
 20000000/21
[1] 952381

55555555/23

[1] 2415459

Thank you

You are confusing the 'printed' representation of the resulting object
with the object itself:

print(20000000/21, digits = 20)

[1] 952380.9523809524

G

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 Dr. Gavin Simpson             [t] +44 (0)20 7679 0522
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 Gower Street, London          [w] http://www.ucl.ac.uk/~ucfagls/
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It seems division with numbers bigger than 10 000 000 doesn't work
 20000000/21
[1] 952381

55555555/23

[1] 2415459

Thank you

Hi bogdanno

First of all look this

all.equal(21*20000000/21,20000000)

[1] TRUE

So de division work correctly

but if I type

all.equal(952381*21,20000000)

[1] "Mean relative difference: 5e-08"

It's not means R division don't work correctly if you use the command

format(20000000/21,digits=22)

[1] "952380.952380952

So the result: 952381 is a round number not a real result of division.
This occur because R print only 7 significants digits in numbers, if you
test

all.equal(21*952380.952380952,20000000)

[1] TRUE

Bernardo Rangel Tura, M.D,MPH,Ph.D
National Institute of Cardiology
Brazil

"TH" == Ted Harding <Ted.Harding at manchester.ac.uk>
    on Sun, 03 May 2009 10:11:04 +0100 (BST) writes:

>> It seems division with numbers bigger than 10 000 000
    >> doesn't work 20000000/21 [1] 952381
    >>> 55555555/23
    >> [1] 2415459
    >> 
    >> Thank you

    TH> I think you are confusing what is displayed with what is
    TH> computed:

    TH>   20000000/21 # [1] 952381 print(20000000/21,17) # [1]
    TH> 952380.9523809524

    TH>   55555555/23 # [1] 2415459 print(55555555/23,17) # [1]
    TH> 2415458.913043478

    TH>   (20000000/21)*21 # [1] 2e+07
    TH> print((20000000/21)*21,17) # [1] 2e+07

    TH>   (55555555/23)*23 # [1] 55555555
    TH> print((55555555/23)*23,17) # [1] 55555555

    TH> Your "numbers bigger than 10 000 000" corresponds to the
    TH> default display of results to 7 significant figures.

    TH> If (as in the above print() statements) you increase
    TH> this, you get more "reasonable"-looking results.

Yes, indeed.
If Bogdanno thinks he wants to always see "all" digits, he
should use something like

  options(digits= 20)

in his R startup setting, e.g. in his Rprofile, see  ?Startup.

Note however:  
     Quite a few experienced R users rather do  *REDUCE* the default number
     of digits printed, rather than enlarge them.
     (I don't)

Martin Maechler, ETH Zurich


    TH> --------------------------------------------------------------------
    TH> E-Mail: (Ted Harding) <Ted.Harding at manchester.ac.uk>
    TH> Fax-to-email: +44 (0)870 094 0861 Date: 03-May-09 Time:
    TH> 10:11:02 ------------------------------ XFMail
    TH> ------------------------------