Re: [R] Help with understanding [[]] [] array, list, matrix referencing
I want to thank everyone for their comments and suggestions. P. Burns'
S Poetry I think will be a lot of help and I thought it was really
poetry:). So will the other references that were provided by I believe
Mr Kane. The other replies provided me some great insights.
If I understand R uses the $ and [[]] like java uses the . (dot)
notation for accessing components of classes and objects. If the java
class or object being accessed by the . notation is specifically a list,
container, vector, or array type you use the element operator which is
the parenthesis in java but R uses [].
This helps be visualize what I am trying to do if I am correct with my
interpretation.
Thank all of you so much.
Joe
Thomas Lumley wrote:
On Tue, 24 Oct 2006, Joe W. Byers wrote:
following code produces a 5 element list of 2X5 random numbers that I
then convert to a 2X5X5 matrix.
cov-matrix(c(.4,-.1,-.1,.3),nrow=2,ncol=2)
rnds-NULL;
for (i in 1:5){
t1-rnorm(5,cov)
t2-rnorm(5,cov)
t3-rbind(t1,t2)
rnds[i]-list(t3)
}
rnds.matrix-array(unlist(rnds),dim=c(2,5,5));
To access the matrix rnds.matrix I use rnds.matrix[x,y,z]. This I
understand.
To access the list I user [[z]][x,y]. This I do not understand. I
found by chance this reference notation in an old mailing list that
helped me.
Yes, this can be confusing. One reason that it is confusing is that the
rules appear to be different (though they aren't) for vectors and lists.
The single bracket [ extracts a subvector, and the double bracket [[
extracts an element. That is, with
a-list(b=1,c=2,d=3)
you can extracts the first element of a,
a[[1]]
[1] 1
or a sublist with the first two elements
a[1:2]
$b
[1] 1
$c
[1] 2
or a sublist with just the first element
a[1]
$b
[1] 1
The same is true for numeric or character vectors, but there an element
and a subvector of length one are the same, so the distinction between [[
and [ is harder to understand.
b-1:10
b[1:2]
[1] 1 2
b[1]
[1] 1
b[[1]]
[1] 1
-thomas
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[R] Help with understanding [[]] [] array, list, matrix referencing
Hi all,
I would greatly appreciate some help understanding how R references
arrays, matrices, lists, and objects using [[]] and []. I have read the
R guides and several tutorials but I am not the fastest kid on the block
so I am still having difficulty understanding this. For examples the
following code produces a 5 element list of 2X5 random numbers that I
then convert to a 2X5X5 matrix.
cov-matrix(c(.4,-.1,-.1,.3),nrow=2,ncol=2)
rnds-NULL;
for (i in 1:5){
t1-rnorm(5,cov)
t2-rnorm(5,cov)
t3-rbind(t1,t2)
rnds[i]-list(t3)
}
rnds.matrix-array(unlist(rnds),dim=c(2,5,5));
To access the matrix rnds.matrix I use rnds.matrix[x,y,z]. This I
understand.
To access the list I user [[z]][x,y]. This I do not understand. I
found by chance this reference notation in an old mailing list that
helped me.
I could use some help in knowing when to use [[]] referencing and when
to use [] referencing. If there is a really good book, webpage, or link
with explanation and examples I would appreciate you forwarding the the
citation.
Thank you
Joe
__
R-help@stat.math.ethz.ch mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] Help with understanding [[]] [] array, list, matrix referencing
Have you tried help([), which gives a good explanation.
On 24/10/06, Joe W. Byers [EMAIL PROTECTED] wrote:
Hi all,
I would greatly appreciate some help understanding how R references
arrays, matrices, lists, and objects using [[]] and []. I have read the
R guides and several tutorials but I am not the fastest kid on the block
so I am still having difficulty understanding this. For examples the
following code produces a 5 element list of 2X5 random numbers that I
then convert to a 2X5X5 matrix.
cov-matrix(c(.4,-.1,-.1,.3),nrow=2,ncol=2)
rnds-NULL;
for (i in 1:5){
t1-rnorm(5,cov)
t2-rnorm(5,cov)
t3-rbind(t1,t2)
rnds[i]-list(t3)
}
rnds.matrix-array(unlist(rnds),dim=c(2,5,5));
To access the matrix rnds.matrix I use rnds.matrix[x,y,z]. This I
understand.
To access the list I user [[z]][x,y]. This I do not understand. I
found by chance this reference notation in an old mailing list that
helped me.
I could use some help in knowing when to use [[]] referencing and when
to use [] referencing. If there is a really good book, webpage, or link
with explanation and examples I would appreciate you forwarding the the
citation.
Thank you
Joe
__
R-help@stat.math.ethz.ch 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.
--
=
David Barron
Said Business School
University of Oxford
Park End Street
Oxford OX1 1HP
__
R-help@stat.math.ethz.ch 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.
Re: [R] Help with understanding [[]] [] array, list, matrix referencing
David,
Yes, I did. I just still do not get it. That is why I ask here.
Hoping someone knew a step by step guide that I could look at. My trial
and error approach takes me hours some days. I currently move most
things in and out of data.frames where I can name the columns and
reference with the $ and a subsetting function, but that is not always
efficient. If I could understand the [ referencing better, my code
would be more efficient and I think faster. Part of my problem is my
SAS background where everything is a flat table and coding is really
sloppy. A data step with a bunch of if-then-else to perform the
calculation where as in matrix format like in R you do things more
compactly. Not always easy to read but efficient and fast.
I appreciate you help.
Thank you
Joe
David Barron wrote:
Have you tried help([), which gives a good explanation.
On 24/10/06, Joe W. Byers [EMAIL PROTECTED] wrote:
Hi all,
I would greatly appreciate some help understanding how R references
arrays, matrices, lists, and objects using [[]] and []. I have read the
R guides and several tutorials but I am not the fastest kid on the block
so I am still having difficulty understanding this. For examples the
following code produces a 5 element list of 2X5 random numbers that I
then convert to a 2X5X5 matrix.
cov-matrix(c(.4,-.1,-.1,.3),nrow=2,ncol=2)
rnds-NULL;
for (i in 1:5){
t1-rnorm(5,cov)
t2-rnorm(5,cov)
t3-rbind(t1,t2)
rnds[i]-list(t3)
}
rnds.matrix-array(unlist(rnds),dim=c(2,5,5));
To access the matrix rnds.matrix I use rnds.matrix[x,y,z]. This I
understand.
To access the list I user [[z]][x,y]. This I do not understand. I
found by chance this reference notation in an old mailing list that
helped me.
I could use some help in knowing when to use [[]] referencing and when
to use [] referencing. If there is a really good book, webpage, or link
with explanation and examples I would appreciate you forwarding the the
citation.
Thank you
Joe
__
R-help@stat.math.ethz.ch 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.
__
R-help@stat.math.ethz.ch 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.
Re: [R] Help with understanding [[]] [] array, list, matrix referencing
Well, as I understand it, with a list [] doesn't return the actual
contents of that element of the list, whereas [[]] does. Compare, for
example rnds[1] + 1 with rnds[[1]] + 1. So, with a list you have to
use the double bracket notation to get to the actual contents of that
element of the list, as opposed to a pointer to the element. With a
vector or a matrix, [[]] doesn't seem to have much use, though you can
use it with a single number, in which case you will get the same
result as [].
There is a separate method for data frames, in which [[]] will give
you a column. So, I think that data[[1]] is the same as data[,1].
Anyway, these rules have always worked for me, though I'm sure others
can give a more sophisticated answer!
On 24/10/06, Joe Byers [EMAIL PROTECTED] wrote:
David,
Yes, I did. I just still do not get it. That is why I ask here.
Hoping someone knew a step by step guide that I could look at. My trial
and error approach takes me hours some days. I currently move most
things in and out of data.frames where I can name the columns and
reference with the $ and a subsetting function, but that is not always
efficient. If I could understand the [ referencing better, my code
would be more efficient and I think faster. Part of my problem is my
SAS background where everything is a flat table and coding is really
sloppy. A data step with a bunch of if-then-else to perform the
calculation where as in matrix format like in R you do things more
compactly. Not always easy to read but efficient and fast.
I appreciate you help.
Thank you
Joe
David Barron wrote:
Have you tried help([), which gives a good explanation.
On 24/10/06, Joe W. Byers [EMAIL PROTECTED] wrote:
Hi all,
I would greatly appreciate some help understanding how R references
arrays, matrices, lists, and objects using [[]] and []. I have read the
R guides and several tutorials but I am not the fastest kid on the block
so I am still having difficulty understanding this. For examples the
following code produces a 5 element list of 2X5 random numbers that I
then convert to a 2X5X5 matrix.
cov-matrix(c(.4,-.1,-.1,.3),nrow=2,ncol=2)
rnds-NULL;
for (i in 1:5){
t1-rnorm(5,cov)
t2-rnorm(5,cov)
t3-rbind(t1,t2)
rnds[i]-list(t3)
}
rnds.matrix-array(unlist(rnds),dim=c(2,5,5));
To access the matrix rnds.matrix I use rnds.matrix[x,y,z]. This I
understand.
To access the list I user [[z]][x,y]. This I do not understand. I
found by chance this reference notation in an old mailing list that
helped me.
I could use some help in knowing when to use [[]] referencing and when
to use [] referencing. If there is a really good book, webpage, or link
with explanation and examples I would appreciate you forwarding the the
citation.
Thank you
Joe
__
R-help@stat.math.ethz.ch 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.
--
=
David Barron
Said Business School
University of Oxford
Park End Street
Oxford OX1 1HP
__
R-help@stat.math.ethz.ch 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.
Re: [R] Help with understanding [[]] [] array, list, matrix referencing
Thank you so very much. I can try this on my own examples.
Much appreciated.
Joe
David Barron wrote:
Well, as I understand it, with a list [] doesn't return the actual
contents of that element of the list, whereas [[]] does. Compare, for
example rnds[1] + 1 with rnds[[1]] + 1. So, with a list you have to
use the double bracket notation to get to the actual contents of that
element of the list, as opposed to a pointer to the element. With a
vector or a matrix, [[]] doesn't seem to have much use, though you can
use it with a single number, in which case you will get the same
result as [].
There is a separate method for data frames, in which [[]] will give
you a column. So, I think that data[[1]] is the same as data[,1].
Anyway, these rules have always worked for me, though I'm sure others
can give a more sophisticated answer!
On 24/10/06, Joe Byers [EMAIL PROTECTED] wrote:
David,
Yes, I did. I just still do not get it. That is why I ask here.
Hoping someone knew a step by step guide that I could look at. My trial
and error approach takes me hours some days. I currently move most
things in and out of data.frames where I can name the columns and
reference with the $ and a subsetting function, but that is not always
efficient. If I could understand the [ referencing better, my code
would be more efficient and I think faster. Part of my problem is my
SAS background where everything is a flat table and coding is really
sloppy. A data step with a bunch of if-then-else to perform the
calculation where as in matrix format like in R you do things more
compactly. Not always easy to read but efficient and fast.
I appreciate you help.
Thank you
Joe
David Barron wrote:
Have you tried help([), which gives a good explanation.
On 24/10/06, Joe W. Byers [EMAIL PROTECTED] wrote:
Hi all,
I would greatly appreciate some help understanding how R references
arrays, matrices, lists, and objects using [[]] and []. I have
read the
R guides and several tutorials but I am not the fastest kid on the
block
so I am still having difficulty understanding this. For examples the
following code produces a 5 element list of 2X5 random numbers that I
then convert to a 2X5X5 matrix.
cov-matrix(c(.4,-.1,-.1,.3),nrow=2,ncol=2)
rnds-NULL;
for (i in 1:5){
t1-rnorm(5,cov)
t2-rnorm(5,cov)
t3-rbind(t1,t2)
rnds[i]-list(t3)
}
rnds.matrix-array(unlist(rnds),dim=c(2,5,5));
To access the matrix rnds.matrix I use rnds.matrix[x,y,z]. This I
understand.
To access the list I user [[z]][x,y]. This I do not understand. I
found by chance this reference notation in an old mailing list that
helped me.
I could use some help in knowing when to use [[]] referencing and
when
to use [] referencing. If there is a really good book, webpage,
or link
with explanation and examples I would appreciate you forwarding
the the
citation.
Thank you
Joe
__
R-help@stat.math.ethz.ch 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.
__
R-help@stat.math.ethz.ch 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.
Re: [R] Help with understanding [[]] [] array, list, matrix referencing
--- Joe Byers [EMAIL PROTECTED] wrote:
David,
Yes, I did. I just still do not get it. That is
why I ask here.
Hoping someone knew a step by step guide that I
could look at. My trial
and error approach takes me hours some days. I
currently move most
things in and out of data.frames where I can name
the columns and
reference with the $ and a subsetting function, but
that is not always
efficient. If I could understand the [ referencing
better, my code
would be more efficient and I think faster. Part of
my problem is my
SAS background where everything is a flat table and
coding is really
sloppy. A data step with a bunch of if-then-else to
perform the
calculation where as in matrix format like in R you
do things more
compactly. Not always easy to read but efficient
and fast.
I appreciate you help.
Thank you
Joe
I'm with you Joe. However you might want to have a
look at chapter 2 of An Introduction to S and The
Hmisc and Design Libraries
Carlos Alzola Harrell availabe in the contributed
material on the CRAN site.
David Barron wrote:
Have you tried help([), which gives a good
explanation.
On 24/10/06, Joe W. Byers [EMAIL PROTECTED]
wrote:
Hi all,
I would greatly appreciate some help
understanding how R references
arrays, matrices, lists, and objects using [[]]
and []. I have read the
R guides and several tutorials but I am not the
fastest kid on the block
so I am still having difficulty understanding
this. For examples the
following code produces a 5 element list of 2X5
random numbers that I
then convert to a 2X5X5 matrix.
cov-matrix(c(.4,-.1,-.1,.3),nrow=2,ncol=2)
rnds-NULL;
for (i in 1:5){
t1-rnorm(5,cov)
t2-rnorm(5,cov)
t3-rbind(t1,t2)
rnds[i]-list(t3)
}
rnds.matrix-array(unlist(rnds),dim=c(2,5,5));
To access the matrix rnds.matrix I use
rnds.matrix[x,y,z]. This I
understand.
To access the list I user [[z]][x,y]. This I do
not understand. I
found by chance this reference notation in an old
mailing list that
helped me.
I could use some help in knowing when to use [[]]
referencing and when
to use [] referencing. If there is a really good
book, webpage, or link
with explanation and examples I would appreciate
you forwarding the the
citation.
Thank you
Joe
__
R-help@stat.math.ethz.ch 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.
__
R-help@stat.math.ethz.ch 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.
__
R-help@stat.math.ethz.ch 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.
Re: [R] Help with understanding [[]] [] array, list, matrix referencing
On Tue, 24 Oct 2006, Joe W. Byers wrote:
following code produces a 5 element list of 2X5 random numbers that I
then convert to a 2X5X5 matrix.
cov-matrix(c(.4,-.1,-.1,.3),nrow=2,ncol=2)
rnds-NULL;
for (i in 1:5){
t1-rnorm(5,cov)
t2-rnorm(5,cov)
t3-rbind(t1,t2)
rnds[i]-list(t3)
}
rnds.matrix-array(unlist(rnds),dim=c(2,5,5));
To access the matrix rnds.matrix I use rnds.matrix[x,y,z]. This I
understand.
To access the list I user [[z]][x,y]. This I do not understand. I
found by chance this reference notation in an old mailing list that
helped me.
Yes, this can be confusing. One reason that it is confusing is that the
rules appear to be different (though they aren't) for vectors and lists.
The single bracket [ extracts a subvector, and the double bracket [[
extracts an element. That is, with
a-list(b=1,c=2,d=3)
you can extracts the first element of a,
a[[1]]
[1] 1
or a sublist with the first two elements
a[1:2]
$b
[1] 1
$c
[1] 2
or a sublist with just the first element
a[1]
$b
[1] 1
The same is true for numeric or character vectors, but there an element
and a subvector of length one are the same, so the distinction between [[
and [ is harder to understand.
b-1:10
b[1:2]
[1] 1 2
b[1]
[1] 1
b[[1]]
[1] 1
-thomas
__
R-help@stat.math.ethz.ch 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.
