[R] read.*: How to read from a URL?

[hadley wickham]

Hi Michael,

In general, I think you should be able to do:

gimage <- read.jpeg(url(gimageloc))

or alternatively use the EBImage from bioconductor which will read
from a url automatically (it also opens a much wider range of file
types)

library(EBImage)
img <- readImage(gimageloc, TrueColor)

Hadley


On Wed, Dec 10, 2008 at 1:17 PM, Michael Friendly <friendly at yorku.ca> wrote:
> The question is how to use a URL in place of a file= argument for
> read.*.functions that do
> not support this internally.
>
> e.g., utils::read.table() and her family all support a file= argument that
> can take a URL
> equally well as a local file.  So, if I have a file on the web, I can
> equally well do
>
>> langren <- read.csv("langrens.csv", header=TRUE)
>> langren <-
>> read.csv("http://euclid.psych.yorku.ca/SCS/Gallery/Private/langrens.csv",
>> header=TRUE)
>
> where the latter is more convenient for posts to this list or distributed
> examples.
> rimage::read.jpeg() doesn't support URLs, and the only way I've found is to
> download the
> image file from a URL to a temp file, in several steps.
> This is probably a more general problem than just read.jpeg,
> so maybe there is a general idiom for this case, or better-- other read.*
> functions could
> be encouraged to support URLs.
>
>> library(rimage)
>> # local file: OK
>> gimage <-
>> read.jpeg("C:/Documents/milestone/images/vanLangren/google-toledo-rome3.jpg")
>>
>> gimageloc <-
>> "http://euclid.psych.yorku.ca/SCS/Gallery/images/Private/Langren/google-toledo-rome3.jpg"
>> dest <- paste(tempfile(),'.jpg', sep='')
>> download.file(gimageloc, dest, mode="wb")
> trying URL
> 'http://euclid.psych.yorku.ca/SCS/Gallery/images/Private/Langren/google-toledo-rome3.jpg'
> Content type 'image/jpeg' length 35349 bytes (34 Kb)
> opened URL
> downloaded 34 Kb
>
>> dest
> [1] "C:\\DOCUME~1\\default\\LOCALS~1\\Temp\\Rtmp9nNTdV\\file5f906952.jpg"
>> #  Is there something simpler??
>> gimage <- read.jpeg(dest)
>
>> #  I thought file() might work, but evidently not.
>> gimage <- read.jpeg(file(gimageloc))
> Error in read.jpeg(file(gimageloc)) : Can't open file.
>>
>
> --
> Michael Friendly     Email: friendly AT yorku DOT ca Professor, Psychology
> Dept.
> York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
> 4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
> Toronto, ONT  M3J 1P3 CANADA
>
> ______________________________________________
> R-help at r-project.org 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.
>



-- 
http://had.co.nz/