R help - Dec 2008 - == operand

Hi,
 
I am trying to compare two values using "==" operand, please take a
look of the following example (I copied ALL what I did here without deleting any
line)
 
>    bb<-1
> cc<-50
> cc==abs(bb+52)
[1] FALSE
> C<-53
> C<-53
> c<-53
> cc==abs(bb+52)
[1] FALSE            
 
I am expecting to see a TRUE here. Then I tried another way,
 
> abs(1+52)
[1] 53
> cc==abs(1+52)
[1] FALSE

Why it is FALSE. Then I tried

> d<-abs(b+52)
Error: object "b" not found
> d<-abs(bb+52)
> d
[1] 53
> c==d
[1] TRUE

Now it is TRUE, but a wired thing is as following,
> c==abs(bb+52)
[1] TRUE

The coding "c==abs(bb+52)" is just the same from the 3line in the top,
why 2 different results? HOWEVER, it is not repeatable, I am glad I did not
close the window.

Also, 
> c<-0.5-0.1
> n<-0.6-0.2
> n==c
[1] FALSE

So, is "==" comparing formula or result?

Thanks,
Renny


      
	[[alternative HTML version deleted]]

Hello,

You assigned 53 to c, not cc. Also, take a look at this:

http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-doesn_0027t-R-think-these-numbers-are-equal_003f


On Tue, Dec 9, 2008 at 9:36 PM, Renny Li <rennyli at yahoo.com>
wrote:
> Hi,
>
> I am trying to compare two values using "==" operand, please take
a look of the following example (I copied ALL what I did here without deleting
any line)
>
>>    bb<-1
>> cc<-50
>> cc==abs(bb+52)
> [1] FALSE
>> C<-53
>> C<-53
>> c<-53
>> cc==abs(bb+52)
> [1] FALSE
>
> I am expecting to see a TRUE here. Then I tried another way,
>
>> abs(1+52)
> [1] 53
>> cc==abs(1+52)
> [1] FALSE
>
> Why it is FALSE. Then I tried
>
>
>> d<-abs(b+52)
> Error: object "b" not found
>> d<-abs(bb+52)
>> d
> [1] 53
>> c==d
> [1] TRUE
>
> Now it is TRUE, but a wired thing is as following,
>> c==abs(bb+52)
> [1] TRUE
>
> The coding "c==abs(bb+52)" is just the same from the 3line in the
top, why 2 different results? HOWEVER, it is not repeatable, I am glad I did not
close the window.
>
> Also,
>> c<-0.5-0.1
>> n<-0.6-0.2
>> n==c
> [1] FALSE
>
> So, is "==" comparing formula or result?
>
> Thanks,
> Renny
>
>
>
>        [[alternative HTML version deleted]]
>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
>

On Tue, Dec 9, 2008 at 5:36 PM, Renny Li <rennyli at yahoo.com>
wrote:
> Hi,
>
> I am trying to compare two values using "==" operand, please take
a look of the following example (I copied ALL what I did here without deleting
any line)
>
>>    bb<-1
>> cc<-50
>> cc==abs(bb+52)
> [1] FALSE
>> C<-53
>> C<-53
>> c<-53
>> cc==abs(bb+52)
> [1] FALSE
cc is 50.  bb is 1.  Why do you expect 50 to equal 1 + 52?  Perhaps
you meant to type cc <- 53 ?

Hadley


-- 
http://had.co.nz/

Renny Li wrote:
> 
> Hi,
> ?
> I am trying to compare two values using "==" operand, please take
a look
> of the following example (I copied ALL what I did here without deleting
> any line)
> ?
>>??? bb<-1
>> cc<-50
>> cc==abs(bb+52)
> [1] FALSE
>> C<-53
>> C<-53
>> c<-53
>> cc==abs(bb+52)
> [1] FALSE??????????? 
> ?
> I am expecting to see a TRUE here. 
> 
Why?  You are modifying the variables C and c, but not cc.
Perhaps you are confused about the == operator, which
doesn't do assignments -- it only tests equality.


Renny Li wrote:
> 
> Then I tried another way,
> ?
>> abs(1+52)
> [1] 53
>> cc==abs(1+52)
> [1] FALSE
> 
> Why it is FALSE.
> 
 Because cc is 50, which isn't equal to 53? 


Renny Li wrote:
> 
>  Then I tried
> 
> 
>> d<-abs(b+52)
> Error: object "b" not found
>> d<-abs(bb+52)
>> d
> [1] 53
>> c==d
> [1] TRUE
> 
> Now it is TRUE, 
> 
Which makes sense because c is 53 and d is 1+52 (i.e., 53)


Renny Li wrote:
> 
> but a wired thing is as following,
>> c==abs(bb+52)
> [1] TRUE
> 
> The coding "c==abs(bb+52)" is just the same from the 3line in the
top, why
> 2 different results? HOWEVER, it is not repeatable, I am glad I did not
> close the window.
> 
It's different, because cc and c are different


Renny Li wrote:
> 
> Also, 
>> c<-0.5-0.1
>> n<-0.6-0.2
>> n==c
> [1] FALSE
> 
For this one, you need to see FAQ 7.31 ...


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