Getting data in R as dataframe from web source

Question

I am trying to load some air pollution background data directly into R as a data.frame using the RCurl package.

The website in question has 3 dropdown boxes to choose options before downloading the .csv file as shown in figure below:

I am trying to select 3 values from the drop down box and download the data using "Download CSV" button directly into R as a data.frame.

I want to download the different combinations of multiple years and multiple pollutants for a specific site.

In other posts on StackOverflow I have come across getForm function from the RCurl package but I don't understand how to control the 3 dropdown boxes with this function.

The URL for the data source is: http://uk-air.defra.gov.uk/data/laqm-background-maps?year=2011

Answer 1

For this website you can construct a url and submit a GET request to simply get the csv:

library(httr)
baseURL <- "http://uk-air.defra.gov.uk/data/laqm-background-maps.php"
queryList <- parse_url(baseURL)
queryList$query <- list("bkgrd-la" = 359, "bkgrd-pollutant" = "no2", "bkgrd-year" = 2011,
                        action = "data", year = 2011, submit = "Download+CSV")
res <- GET(build_url(queryList), write_disk("temp.csv"))

You can get the codes for the form by parsing the original page:

library(XML)
doc <- htmlParse("http://uk-air.defra.gov.uk/data/laqm-background-maps?year=2011")
councils <- doc["//*[@id='bkgrd-la']/option", fun = function(x){
  data.frame(value = xmlGetAttr(x, "value"), council = xmlValue(x))
  }]
councils <- do.call(rbind.data.frame, councils)
> head(councils)
value                      council
1   359        Aberdeen City Council
2   360        Aberdeenshire Council
3     1        Adur District Council
4     2    Allerdale Borough Council
5     4 Amber Valley Borough Council
6   401      Anglesey County Council

pollutants <- doc["//*[@id='bkgrd-pollutant']/option", fun = function(x){
  data.frame(value = xmlGetAttr(x, "value"), council = xmlValue(x))
}]
pollutants <- do.call(rbind.data.frame, pollutants)
> head(pollutants)
value council
1   no2     NO2
2   nox     NOx
3  pm10    PM10
4  pm25   PM2.5
5   no2     NO2
6   nox     NOx

etc...