[R] how to create a histogram from a matrix?

[Peter Alspach]

Tena koe Gabriele

read.table() creates a data frame not a matrix.  The distinction is
important.  A data frame is a special kind of list: it is a list of
column vectors all of the same length.  Because it is a list, each
column can be of a different type (i.e., integer, numeric, character,
factor etc).  A matrix is a vector with a dim(ension) attribute and as
such all elements must be of the same type.  Try:

library(lattice)
testData <- rnorm(100)
histogram(testData)  # should be ok
testData <- as.data.frame(testData)
histogram(testData)  # will generate an error
testData <- unlist(testData)
histogram(testData) # should be ok

HTH ....

Peter Alspach

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Zoppoli, 
> Gabriele (NIH/NCI) [G]
> Sent: Friday, 29 January 2010 4:56 p.m.
> To: r-help at r-project.org
> Subject: [R] how to create a histogram from a matrix?
> 
> 
> Hi,
> 
> I'm trying to create a frequency histogram for all the values 
> in a table, but when I try to do so, an error is returned, 
> saying that I cannot create a histogram with an obkect of 
> that class. Here's what I do:
> 
> >library(lattice)
> >table<-read.table("C:/.../table",header=TRUE,sep="\t")
> >histogram(table)
> 
> Please help me!!!
> 
> Thanks
> 
> Gabriele Zoppoli, MD
> Ph.D. Fellow, Experimental and Clinical Oncology and 
> Hematology, University of Genova, Genova, Italy Guest 
> Researcher, LMP, NCI, NIH, Bethesda MD
> 
> Work: 301-451-8575
> Mobile: 301-204-5642
> Email: zoppolig at mail.nih.gov
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