R help - Apr 2012 - puzzling Date math result

Hi,

I cannot make a reproducible example easily for my problem, so I'll
describe it as best as I can.

I merged 2 dataframes but was surprised when one line on the x
dataframe did not get a match in the y dataframe, because I knew such
a match existed. There was only one "by" variable in the merge, in
Date format:

in x:
 $ p?riode    : Date, format: "2009-06-09" "2009-07-09" ...

in y:
 $ date       : Date, format: "2009-05-12" "2009-06-09" ?

I extracted the date that did not match into variables a (from x) and
b (from y):
> a=test1$p?riode[21]
> b=test2$date[22]
> a
[1] "2011-04-06"
> b
[1] "2011-04-06"

and then this very puzzling situation:
a==b
[1] FALSE
> as.integer(a)
[1] 15070
> as.integer(b)
[1] 15070
> as.integer(a)==as.integer(b)
[1] TRUE

Thanks in advance for an explanation or a suggestion to further study
this puzzle,

Denis
sessionInfo()
R version 2.15.0 (2012-03-30)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)

locale:
[1] fr_CA.UTF-8/en_US.UTF-8/fr_CA.UTF-8/C/fr_CA.UTF-8/fr_CA.UTF-8

attached base packages:
[1] splines   stats     graphics  grDevices utils     datasets  methods
[8] base

other attached packages:
 [1] doBy_4.5.2       MASS_7.3-17      snow_0.3-8       lme4_0.999375-42
 [5] Matrix_1.0-6     lattice_0.20-6   multcomp_1.2-12  mvtnorm_0.9-9992
 [9] R2HTML_2.2       survival_2.36-12 gdata_2.8.2

loaded via a namespace (and not attached):
[1] grid_2.15.0   gtools_2.6.2  nlme_3.1-103  stats4_2.15.0 tools_2.15.0

On Tue, 17 Apr 2012 10:44:40 -0400, Denis Chabot wrote: 
> Hi,
>
> I cannot make a reproducible example easily for my problem, so I'll
>
describe it as best as I can.

YOU KIND OF NEED ONE...
>>
a=test1$période[21]
> 
>> b=test2$date[22]
> a f
> argin-left:5px;
width:100%">b 
> 
> [1] "2011-04-06"
> 
>> 
THIS IS WHY YOU NEED TO
GIVE US A REPRODUCABLE MEANS BECAUSE IF I SIMPLY DO A="2011-04-06" AND
B="2011-04-06" I'M GOING TO GET A==B TRUE

WHERE IS THE DATA IN THE DF'S
BEING SOURCED FROM? IS IT A DATABASE? COULD THERE BE DIFFERENT DATA
DEFINITIONS? IS ITS A CSV FILE ETC? 

and then thi> ft:#1010ff 2px
solid; margin-left:5px; width:100%">as.integer(a)
> 
> [1] 15070
> 
>>
as.integer(b)
> 
> [1] 15070
> 
> SUGGESTION THAT MIGHT POINT YOU IN A
DIRECTION...
> 
> as.integer (15070)
pre> 

as.integer (15070.1)

[1]
15070

as.integer (15070)==as.integer(15070.1)

[1]
TRUE

15070==15070.1

[1] FALSE

SECOND SUGGESTION WOULD BE TO DROP THE
É NO IDEA WHY THAT WOULD CAUSE A PROBLEM (OR WHERE), BUT ANYTHING THATS
NOT A-Z OR A-Z ONLY INTRODUCES A POTENTIAL EXTRA HEADACHE...

 
as.integer(a)==as.integer(b) 
> 
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