Displaying 20 results from an estimated 5000 matches similar to: "prcomp vs. princomp vs fast.prcomp"
2009 Oct 19
2
What is the difference between prcomp and princomp?
Some webpage has described prcomp and princomp, but I am still not
quite sure what the major difference between them is. Can they be used
interchangeably?
In help, it says
'princomp' only handles so-called R-mode PCA, that is feature
extraction of variables. If a data matrix is supplied (possibly
via a formula) it is required that there are at least as many
units as
2006 Mar 25
1
Suggest patch for princomp.formula and prcomp.formula
Dear all,
perhaps I am using princomp.formula and prcomp.formula in a way that
is not documented to work, but then the documentation just says:
formula: a formula with no response variable.
Thus, to avoid a lot of typing, it would be nice if one could use '.'
and '-' in the formula, e.g.
> library(DAAG)
> res <- prcomp(~ . - case - site - Pop - sex, possum)
2009 Nov 25
1
which to trust...princomp() or prcomp() or neither?
According to R help:
princomp() uses eigenvalues of covariance data.
prcomp() uses the SVD method.
yet when I run the (eg., USArrests) data example and compare with my own
"hand-written" versions of PCA I get what looks like the opposite.
Example:
comparing the variances I see:
Using prcomp(USArrests)
-------------------------------------
Standard deviations:
[1] 83.732400 14.212402
2006 Jun 26
1
princomp and prcomp confusion
When I look through archives at
https://stat.ethz.ch/pipermail/r-help/2003-October/040525.html
I see this:
Liaw, Andy wrote:
>In the `Detail' section of ?princomp:
>
>princomp only handles so-called Q-mode PCA, that is feature extraction of
>variables. If a data matrix is supplied (possibly via a formula) it is
>required that there are at least as many units as variables. For
2004 Nov 03
2
Princomp(), prcomp() and loadings()
In comparing the results of princomp and prcomp I find:
1. The reported standard deviations are similar but about 1% from
each other, which seems well above round-off error.
2. princomp returns what I understand are variances and cumulative
variances accounted for by each principal component which are
all equal. "SS loadings" is always 1.
3. Same happens
2012 Aug 23
1
Accessing the (first or more) principal component with princomp or prcomp
Hi ,
To my knowledge, there're two functions that can do principal component
analysis, princomp and prcomp.
I don't really know the difference; the only thing I know is that when
the sample size < number of variable, only prcomp will work. Could someone
tell me the difference or where I can find easy-to-read reference?
To access the first PC using princomp:
2008 Nov 03
1
Input correlation matrix directly to princomp, prcomp
Hello fellow Rers,
I have a no-doubt simple question which is turning into a headache so
would be grateful for any help.
I want to do a principal components analysis directly on a correlation
matrix object rather than inputting the raw data (and specifying cor =
TRUE or the like). The reason behind this is I need to use polychoric
correlation coefficients calculated with John Fox's
2000 Dec 01
1
simple (NEWBIE) question re: prcomp or princomp
Hi,
I am a new user of R, and apologize beforehand for the simplistic nature of this question:
I ran prcomp on a data set with 4 variables, and am able to see the summary information (variance contribution, rotation matrix, plots, etc.). However, I'd also like to extract the actual values of the principal components (PC) corresponding to each sample. I've looked in the help, on-line
2009 Mar 08
2
prcomp(X,center=F) ??
I do not understand, from a PCA point of view, the option center=F
of prcomp()
According to the help page, the calculation in prcomp() "is done by a
singular value decomposition of the (centered and possibly scaled) data
matrix, not by using eigen on the covariance matrix" (as it's done by
princomp()) .
"This is generally the preferred method for numerical accuracy"
2003 Oct 16
1
princomp with more coloumns than rows: why not?
As of R 1.7.0, princomp no longer accept matrices with more coloumns
than rows. I'm curious: Why was this decision made?
I work a lot with data where more coloumns than rows is more of a rule
than an exception (for instance spectroscopic data). To me, princomp
have two advantages above prcomp: 1) It has a predict method, and 2)
it has a biplot method.
A biplot method shouldn't be too
2005 Aug 03
3
prcomp eigenvalues
Hello,
Can you get eigenvalues in addition to eigevectors using prcomp? If so how?
I am unable to use princomp due to small sample sizes.
Thank you in advance for your help!
Rebecca Young
--
Rebecca Young
Graduate Student
Ecology & Evolutionary Biology, Badyaev Lab
University of Arizona
1041 E Lowell
Tucson, AZ 85721-0088
Office: 425BSW
rlyoung at email.arizona.edu
(520) 621-4005
2012 May 23
1
prcomp with previously scaled data: predict with 'newdata' wrong
Hello folks,
it may be regarded as a user error to scale() your data prior to prcomp() instead of using its 'scale.' argument. However, it is a user thing that may happen and sounds a legitimate thing to do, but in that case predict() with 'newdata' can give wrong results:
x <- scale(USArrests)
sol <- prcomp(x)
all.equal(predict(sol), predict(sol, newdata=x))
## [1]
2011 Nov 04
1
How to use 'prcomp' with CLUSPLOT?
Hello,
I have a large data set that has more columns than rows (sample data below). I am trying to perform a partitioning cluster analysis and then plot that using pca. I have tried using CLUSPLOT(), but that only allows for 'princomp' where I need 'prcomp' as I do not want to reduce my columns. Is there a way to edit the CLUSPLOT() code to use 'prcomp', please?
#
2010 Nov 10
2
prcomp function
Hello,
I have a short question about the prcomp function. First I cite the
associated help page (help(prcomp)):
"Value:
...
SDEV the standard deviations of the principal components (i.e., the square
roots of the eigenvalues of the covariance/correlation matrix, though the
calculation is actually done with the singular values of the data matrix).
ROTATION the matrix of variable loadings
2005 Mar 24
1
RE: [R] Mapping actual to expected columns for princomp object
[Re-directing to R-devel, as I think this needs changes to the code.]
Can I suggest a modification to stats:predict.princomp so that it will check
for column (variable) names?
In src/library/stats/R/princomp-add.R, insert the following after line 4:
if (!is.null(cn <- names(object$center))) newdata <- newdata[, cn]
Now Dana's example looks like:
> predict(pca1, frz)
Error in
2000 Oct 03
3
prcomp compared to SPAD
Hi !
I've used the example given in the documentation for the prcomp function
both in R and SPAD to compare the results obtained.
Surprisingly, I do not obtain the same results for the coordinates of
the principal composantes with these two softwares.
using USArrests data I obtain with R :
> summary(prcomp(USArrests))
Importance of components:
PC1 PC2
2000 Jan 31
1
Feature requests for princomp(.) : Allow cor() specifications
(all in subject).
If I want to do a PC analysis in a situation with missing data,
I may want to have same flexibility as with "cor(.)",
e.g., I may want
princomp(x, ..., use.obs = "pairwise.complete")
Actually, I may want even more flexibility.
Currently,
princomp(.)
has
if (cor)
cv <- get("cor", envir = .GlobalEnv)(z)
else cv <-
2006 Nov 16
1
Problems with principal components analysis PCA with prcomp
Dear friends,
I am beginning to use R software in my academic research and I'm having some
problems regarding the use of PCA.
I have a table with 24445 rows and 9 columns, and I used the function
prcomp() to do the analysis.
Working with an example?:
x<-read.table("test.txt", header=T)
row.names(x)<-x[,1]
x<-x[,-1]
require(stats)
pca<-prcomp(x, scale=T)
names(pca)
##
1998 Apr 02
2
prcomp
I've noticed that the arguments and result list of prcomp in the mva package
(with 61.1) are not quite the same as in the Blue Book and in Splus. Is this
intentional or can I change it? If I change it who should I send the code to?
Paul Gilbert
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r-devel mailing list -- Read
2009 May 04
1
how to display case names in biplot.prcomp?
hey,
im trying hard to display names (given in a seperate variable) instead
of "case numbers" in a pca plot (by biplot of a prcomp output). somebody
could help me with this?
lukas