[R] Downloading data from from internet

[Duncan Temple Lang]

Bogaso wrote:
> Thank you so much for those helps. However I need little more help. In the
> site
> "http://www.rateinflation.com/consumer-price-index/usa-historical-cpi.php"
> if I scroll below then there is an option "Historical CPI Index For USA"
> Next if I click on "Get Data" then another table pops-up, however without
> any significant change in address bar. This tables holds more data starting
> from 1999. Can you please help me how to get the values of this table?
> 


Hi again

Well, this is a little bit more involved, as this is an HTML form
and so we need to be able to emulate submitting a form with
values for the different parameters the form expects, along with
ensuring they are correct inputs.  Ordinarily, this would involve
looking at the source of the HTML document, finding the relevant
<form> element, getting its action attribute, and all its inputs
and figuring out the possible inputs.  This is "straightforward"
but involved. But we have an R package that does this reasonably
well in an automated form. This is the RHTMLForms from the
www.omegahat.org/R repository.

We can use this with
 install.packages("RHTMLForms", repos = "http://www.omegahat.org/R")

Then

library(RHTMLForms)

ff = getHTMLFormDescription("http://www.rateinflation.com/consumer-price-index/usa-historical-cpi.php")

# The form we want is the third one. We can determine this
# from the names of the parameters.
# So we request that this form description be turned into an R function

g = createFunction(ff[[3]])

  # Now we call this.
xx = g("2001", "2008")


  # This returns the content of an HTML document
  # so we parse it and then pass this to readHTMLTable()
  # This is why we have methods for

library(XML)
doc = htmlParse(xx, asText = TRUE)
tbls = readHTMLTable(doc)

  # we want the last of the tables.
tbls[[length(tbls)]]


So hopefully that helps solve your problem and introduces another Omegahat package that
we hope people find through Google. The RHTMLForms package is an approach to the
poor-man's Web services - HTML forms- rather than REST and SOAP that are becoming more relevant
each day.  The RCurl and SSOAP address the latter.

  D.





> Thanks
> 
> 
> Duncan Temple Lang wrote:
>>
>> Thanks for explaining this, Charlie.
>>
>> Just for completeness and to make things a little easier,
>> the XML package has a function named readHTMLTable()
>> and you can call it with a URL and it will attempt
>> to read all the tables in the page.
>>
>>  tbls =
>> readHTMLTable('http://www.rateinflation.com/consumer-price-index/usa-cpi.php')
>>
>> yields a list with 10 elements, and the table of interest with the data is
>> the 10th one.
>>
>>  tbls[[10]]
>>
>> The function does the XPath voodoo and sapply() work for you and uses some
>> heuristics.
>> There are various controls one can specify and also various methods for
>> working
>> with sub-parts of the HTML document directly.
>>
>>   D.
>>
>>
>>
>> cls59 wrote:
>>>
>>> Bogaso wrote:
>>>> Hi all,
>>>>
>>>> I want to download data from those two different sources, directly into
>>>> R
>>>> :
>>>>
>>>> http://www.rateinflation.com/consumer-price-index/usa-cpi.php
>>>> http://eaindustry.nic.in/asp2/list_d.asp
>>>>
>>>> First one is CPI of US and 2nd one is WPI of India. Can anyone please
>>>> give
>>>> any clue how to download them directly into R. I want to make them zoo
>>>> object for further analysis.
>>>>
>>>> Thanks,
>>>>
>>> The following site did not load for me:
>>>
>>> http://eaindustry.nic.in/asp2/list_d.asp
>>>
>>> But I was able to extract the table from the US CPI site using Duncan
>>> Temple
>>> Lang's XML package:
>>>
>>>   library(XML)
>>>
>>>
>>> First, download the website into R:
>>>
>>>   html.raw <- readLines(
>>> 'http://www.rateinflation.com/consumer-price-index/usa-cpi.php' )
>>>
>>> Then, convert to an HTML object using the XML package:
>>>
>>>   html.data <- htmlTreeParse( html.raw, asText = T, useInternalNodes = T
>>> )
>>>
>>> A quick scan of the page source in the browser reveals that the table you
>>> want is encased in a div with a class of "dynamicContent"-- we will use a
>>> xpath specification[1] to retrieve all rows in that table:
>>>
>>>   table.html <- getNodeSet( html.data,
>>> '//div[@class="dynamicContent"]/table/tr' )
>>>
>>> Now, the data values can be extracted from the cells in the rows using a
>>> little sapply and xpathXpply voodoo:
>>>
>>>   table.data <- t( sapply( table.html, function( row ){
>>>
>>>     row.data <-  xpathSApply( row, './td', xmlValue )
>>>     return( row.data)
>>>
>>>   }))
>>>
>>>
>>> Good luck!
>>>
>>> -Charlie
>>>  
>>>   [1]:  http://www.w3schools.com/XPath/xpath_syntax.asp
>>>
>>> -----
>>> Charlie Sharpsteen
>>> Undergraduate
>>> Environmental Resources Engineering
>>> Humboldt State University
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>