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Stephen Liu

2010-Nov-04 05:50 UTC

[R] Logical vectors

Hi folks,

Pls help me to understand follow;

An Introduction to R

2.4 Logical vectors
http://cran.r-project.org/doc/manuals/R-intro.html#R-and-statistics

1)> x
[1] 1 2 3 4 5> temp <- x != 1
> temp
[1] FALSE  TRUE  TRUE  TRUE  TRUE> 

2)> x
[1] 1 2 3 4 5> temp <- x > 1
> temp[1] FALSE  TRUE  TRUE  TRUE  TRUE


Why NOT> temp[1] TRUE  FALSE  FALSE FALSE  FALSE

?


TIA

B.R.
Stephen L

Gerrit Eichner

2010-Nov-04 06:34 UTC

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[R] Logical vectors

On Wed, 3 Nov 2010, Stephen Liu wrote:

[snip]
> 2)
>> x
> [1] 1 2 3 4 5
>> temp <- x > 1
>> temp
> [1] FALSE  TRUE  TRUE  TRUE  TRUE
>
>
> Why NOT
>> temp
> [1] TRUE  FALSE  FALSE FALSE  FALSE
>
> ?

Maybe because of the definition of ">" (greater (!) than)? Or do
you
expect 1 to be greater than 1 and not greater than 2, 3, 4, and 5?

  Regards  --  Gerrit

---------------------------------------------------------------------
AOR Dr. Gerrit Eichner               Mathematical Institute, Room 212
gerrit.eichner at math.uni-giessen.de   Justus-Liebig-University Giessen
Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany
Fax: +49-(0)641-99-32109        http://www.uni-giessen.de/cms/eichner

Joshua Wiley

2010-Nov-04 06:46 UTC

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[R] Logical vectors

On Wed, Nov 3, 2010 at 10:50 PM, Stephen Liu <satimis at yahoo.com>
wrote:> Hi folks,
>
> Pls help me to understand follow;
>
> An Introduction to R
>
> 2.4 Logical vectors
> http://cran.r-project.org/doc/manuals/R-intro.html#R-and-statistics
>
> 1)
>> x
> [1] 1 2 3 4 5
a vector, x, is defined with 5 elements, {1, 2, 3, 4, 5}
>> temp <- x != 1
perform the logical test that x does not equal 1 returning either TRUE or FALSE.

1 = 1 so TRUE, 2 != 1 so FALSE, etc.  next we assign *the results* of
the logical test to the vector 'temp'
>> temp
> [1] FALSE ?TRUE ?TRUE ?TRUE ?TRUE
print the vector to screen
>>
>
>
> 2)
>> x
> [1] 1 2 3 4 5
note that x has not changed here, we assigned to temp, not to x.
>> temp <- x > 1
now we assign the results of the logical test, x > 1

{1 = 1 so FALSE, 2 > 1 so TRUE, 3 > 1 so TRUE, 4 > 1 so TRUE, 5 > 1
so TRUE}

we assign these results to a vector, 'temp'.  This *new* assignment
overwrites the old vector 'temp'
>> temp
> [1] FALSE ?TRUE ?TRUE ?TRUE ?TRUE
print temp to screen, this is the results of our second logical test (x > 1).
>
>
> Why NOT
>> temp
> [1] TRUE ?FALSE ?FALSE FALSE ?FALSE
My best guess of where you got confused is that we assigned the
results to 'temp', so 'x' remained unchanged {1, 2, 3, 4, 5}, or
that
you confused '<-' which is the assignment operator in R, to
"less than
negative..." *OR*  "less than or equal".  We could write this
equivalently:
> 1:5 > 1[1] FALSE  TRUE  TRUE  TRUE  TRUE

this was the logical test, whose results were assigned to the vector,
"temp".
> assign(x = "temp", value = 1:5 > 1)
using the assign function (not often recommended) to avoid any
confusion with the assignment operator, "<-".
> temp[1] FALSE  TRUE  TRUE  TRUE  TRUE

print to screen

HTH,

Josh
>
> ?
>
>
> TIA
>
> B.R.
> Stephen L
>
>
>
> ______________________________________________
> 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.


-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/

Stephen Liu

2010-Nov-04 08:16 UTC

head link

[R] Logical vectors

Hi Gerrit,

Thanks for your advice.


In;

2.4 Logical vectors
http://cran.r-project.org/doc/manuals/R-intro.html#R-and-statistics

It states:-

The logical operators are <, <=, >, >=, == for exact equality and !=
for
inequality ........
>    # exact equality!=   # inequality


I did follows;
> x <- 1:5
> x[1] 1 2 3 4 5
> temp <- x != 1
> temp[1] FALSE  TRUE  TRUE  TRUE  TRUE

That is correct.

> rm(temp)
> 
> temp <- x > 1
> temp[1] FALSE  TRUE  TRUE  TRUE  TRUE

That seems not correct.

My understanding is;> [1] TRUE  FALSE  FALSE FALSE  FALSE
B.R.
Stephen L





----- Original Message ----
From: Gerrit Eichner <Gerrit.Eichner at math.uni-giessen.de>
To: Stephen Liu <satimis at yahoo.com>
Cc: r-help at r-project.org
Sent: Thu, November 4, 2010 2:34:55 PM
Subject: Re: [R] Logical vectors

On Wed, 3 Nov 2010, Stephen Liu wrote:

[snip]
> 2)
>> x
> [1] 1 2 3 4 5
>> temp <- x > 1
>> temp
> [1] FALSE  TRUE  TRUE  TRUE  TRUE
>
>
> Why NOT
>> temp
> [1] TRUE  FALSE  FALSE FALSE  FALSE
>
> ?

Maybe because of the definition of ">" (greater (!) than)? Or do
you
expect 1 to be greater than 1 and not greater than 2, 3, 4, and 5?

  Regards  --  Gerrit

---------------------------------------------------------------------
AOR Dr. Gerrit Eichner               Mathematical Institute, Room 212
gerrit.eichner at math.uni-giessen.de   Justus-Liebig-University Giessen
Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany
Fax: +49-(0)641-99-32109        http://www.uni-giessen.de/cms/eichner
---------------------------------------------------------------------

Gerrit Eichner

2010-Nov-04 08:56 UTC

head link

[R] Logical vectors

On Thu, 4 Nov 2010, Stephen Liu wrote:

[snip]
> In;
>
> 2.4 Logical vectors
> http://cran.r-project.org/doc/manuals/R-intro.html#R-and-statistics
>
> It states:-
>
> The logical operators are <, <=, >, >=, == for exact equality
and != for
> inequality ........
>
>>    # exact equality
> !=   # inequality
[snip]


Hello, Stephen,

in my understanding of the sentence

"The logical operators are <, <=, >, >=, == for exact equality
and != for
inequality ........"

the phrase "exact equality" refers to the operator "==", i.
e. to the last
element "==" in the enumeration (<, <=, >, >=, ==), and
not to its first.

  Regards  --  Gerrit

---------------------------------------------------------------------
AOR Dr. Gerrit Eichner               Mathematical Institute, Room 212
gerrit.eichner at math.uni-giessen.de   Justus-Liebig-University Giessen
Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany
Fax: +49-(0)641-99-32109        http://www.uni-giessen.de/cms/eichner

Stephen Liu

2010-Nov-04 09:29 UTC

head link

[R] Logical vectors

H Gerrit,
> the phrase "exact equality" refers to the operator
"==", i. e. to the last
> element "==" in the enumeration (<, <=, >, >=, ==),
and not to its first.
> x <- 1:5
> x[1] 1 2 3 4 5
> temp <-x == 1
> temp[1]  TRUE FALSE FALSE FALSE FALSE

I got it thanks.

B.R.
Stephen L




----- Original Message ----
From: Gerrit Eichner <Gerrit.Eichner at math.uni-giessen.de>
To: Stephen Liu <satimis at yahoo.com>
Cc: r-help at r-project.org
Sent: Thu, November 4, 2010 4:56:42 PM
Subject: Re: [R] Logical vectors

On Thu, 4 Nov 2010, Stephen Liu wrote:

[snip]
> In;
>
> 2.4 Logical vectors
> http://cran.r-project.org/doc/manuals/R-intro.html#R-and-statistics
>
> It states:-
>
> The logical operators are <, <=, >, >=, == for exact equality
and != for
> inequality ........
>
>>    # exact equality
> !=   # inequality
[snip]


Hello, Stephen,

in my understanding of the sentence

"The logical operators are <, <=, >, >=, == for exact equality
and != for
inequality ........"

the phrase "exact equality" refers to the operator "==", i.
e. to the last
element "==" in the enumeration (<, <=, >, >=, ==), and
not to its first.

  Regards  --  Gerrit

---------------------------------------------------------------------
AOR Dr. Gerrit Eichner               Mathematical Institute, Room 212
gerrit.eichner at math.uni-giessen.de   Justus-Liebig-University Giessen
Tel: +49-(0)641-99-32104          Arndtstr. 2, 35392 Giessen, Germany
Fax: +49-(0)641-99-32109        http://www.uni-giessen.de/cms/eichner
---------------------------------------------------------------------

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