Singular design matrix in rq

set.seed(1)
x <- c(rep(0, 20), 1:15)
y <- sort(rnorm(length(x)))
rq(y~bs(x, df=15), tau=.5)

# lm deals with a singular design matrix by dropping columns from the model
lm(y~bs(x, df=15))

svd(cbind(1, bs(x, df=15)))$d # design matrix is not full rank

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
Of Jonathan Greenberg
Sent: Friday, April 19, 2013 6:29 AM
To: Koenker, Roger W
Cc: r-help
Subject: Re: [R] Singular design matrix in rq

Roger:

Doh!  Just realized I had that error in the code -- raw_data is the same as
mydata, so it should be:

mydata <- read.csv("singular.csv")
plot(mydata$predictor,mydata$response)
# A big cloud of points, nothing too weird
summary(mydata)
# No NAs:

#       X            response         predictor
# Min.   :    1   Min.   :    0.0   Min.   : 0.000
# 1st Qu.:12726   1st Qu.:  851.2   1st Qu.: 0.000
# Median :25452   Median : 2737.0   Median : 0.000
# Mean   :25452   Mean   : 3478.0   Mean   : 5.532
# 3rd Qu.:38178   3rd Qu.: 5111.6   3rd Qu.: 5.652
# Max.   :50903   Max.   :26677.8   Max.   :69.342

fit_spl <- rq(response ~ bs(predictor,df=15),tau=1,data=mydata)
# Error in rq.fit.br(x, y, tau = tau, ...) : Singular design matrix

--j



On Fri, Apr 19, 2013 at 8:15 AM, Koenker, Roger W <rkoenker at illinois.edu>wrote:

Jonathan,

This is not what we call a reproducible example... what is raw_data?  Does
it have something to do with mydata?
what is i?

Roger

url:    www.econ.uiuc.edu/~roger            Roger Koenker
email    rkoenker at uiuc.edu            Department of Economics
vox:     217-333-4558                University of Illinois
fax:       217-244-6678                Urbana, IL 61801

On Apr 16, 2013, at 2:58 PM, Greenberg, Jonathan wrote:

Quantreggers:

I'm trying to run rq() on a dataset I posted at:

https://docs.google.com/file/d/0B8Kij67bij_ASUpfcmJ4LTFEUUk/edit?usp=sharing

(it's a 1500kb csv file named "singular.csv") and am getting the

following error:

mydata <- read.csv("singular.csv")
fit_spl <- rq(raw_data[,1] ~ bs(raw_data[,i],df=15),tau=1)

Error in rq.fit.br(x, y, tau = tau, ...) : Singular design matrix

Any ideas what might be causing this or, more importantly, suggestions

for how to solve this?  I'm just trying to fit a smoothed hull to the top
of the data cloud (hence the large df).

Thanks!

--jonathan


--
Jonathan A. Greenberg, PhD
Assistant Professor
Global Environmental Analysis and Remote Sensing (GEARS) Laboratory
Department of Geography and Geographic Information Science
University of Illinois at Urbana-Champaign
607 South Mathews Avenue, MC 150
Urbana, IL 61801
Phone: 217-300-1924
http://www.geog.illinois.edu/~jgrn/
AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307, Skype: jgrn3007

--
Jonathan A. Greenberg, PhD
Assistant Professor
Global Environmental Analysis and Remote Sensing (GEARS) Laboratory
Department of Geography and Geographic Information Science
University of Illinois at Urbana-Champaign
607 South Mathews Avenue, MC 150
Urbana, IL 61801
Phone: 217-300-1924
http://www.geog.illinois.edu/~jgrn/
AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307, Skype: jgrn3007

	[[alternative HTML version deleted]]