Re: question on cor function

[David L Lorenz <lorenz@usgs.gov>]

Walt,
  My guess is that there are missing
values elsewhere in each data set, so you are getting different rows when
you select only the first column in each data set.
  Try cor(na.omit(pat)[,1], na.omit(att)[,1])
Dave

From:	"Data Analytics Corp." <dataanalytics@earthlink.net>
To:	s-news@lists.biostat.wustl.edu
Date:	05/07/2009 10:15 AM
Subject:	[S] question on cor function
Sent by:	s-news-owner@lists.biostat.wustl.edu

---

Hi,

I'm confused about what the cor function is producing.  I have two
data 
frames: pat and att.  Each has 417 rows with missing data.  The
first, 
pat, has 4 columns; att has 30.  I want the correlations between each
column of pat with each column of att.  My results should be a 30
by 4 
matrix.  I used at first

t(cor(pat, att, na.method = "omit"))

and got my 30X4 matrix.  The first cell, which should be for the 
correlation between pat[, 1] and att[, 1] is -0.24399252  But then,
just 
for a check, I did cor(pat[, 1], att[, 1], na.method = "omit")
and got a 
different answer!  I got 0.001174417.  What's going on???  According
to 
the Help file, the answer for my first statement with the transpose 
should be "a matrix such that the [i,j] element is the covariance
(correlation) of x[,i] and either y[,j] or x[,j]. "  So the [1,1]
answer 
should be the correlation between pat[, 1] and att[, 1] - but it's not.
 
What am I missing?? Am I just not seeing the obvious??   I'm using
S+8.0 
on a Vista machine.

Thanks,

Walt



-- 
________________________

Walter R. Paczkowski, Ph.D.
Data Analytics Corp.
44 Hamilton Lane
Plainsboro, NJ 08536
________________________
(V) 609-936-8999
(F) 609-936-3733
dataanalytics@earthlink.net
www.dataanalyticscorp.com

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