readHTMLTable {XML} | R Documentation

## Read data from one or more HTML tables

### Description

This function and its methods provide somewhat robust methods for extracting data from HTML tables in an HTML document. One can read all the tables in a document given by filename or URL, or having already parsed the document via `htmlParse`. Alternatively, one can specify an individual `<table>` node in the document.

The methods attempt to do some heuristic computations to determine the header labels for the columns, the name of the table, etc.

### Usage

    readHTMLTable(doc, header = xmlName(node) == "table" && ("thead" %in% names(node) || length(getNodeSet(node, "./tr[1]/th")) > 0),
                  colClasses = NULL, skip.rows = integer(), trim = TRUE, elFun = xmlValue, as.data.frame = TRUE, ...)

### Arguments

`doc` | the HTML document which can be a file name or a URL or an already parsed `HTMLInternalDocument`, or an HTML node of class `XMLInternalElementNode`.
`header` | either a logical value indicating whether the table has column labels, e.g. the first row or a `thead`, or alternatively a character vector giving the names to use for the resulting columns.
`colClasses` |
`skip.rows` |
`trim` | a logical value indicating whether to remove leading and trailing white space from the content cells.
`elFun` | a function which, if specified, is called when converting each cell. Currently, only the node is specified. In the future, we might additionally pass the index of the column so that the function has some context, e.g. whether the value is a row label or a regular value, or if the caller knows the type of columns.
`as.data.frame` | a logical value indicating whether to turn the resluting table(s) into data frames or leave them as matrices.
`...` | currently additional parameters that are passed on to `as.data.frame` if `as.data.frame` is `TRUE`. We may change this to use these as additional arguments for calls to `elFun`.

### Value

If the document (either by name or parsed tree) is specified, the return vale is a list of data frames or matrices. If a single HTML node is provided

### Author(s)

Duncan Temple Lang

### References

HTML4.0 specification

### See Also

`htmlParse` `getNodeSet` `xpathSApply`

### Examples

     u = "http://en.wikipedia.org/wiki/World_population"

     tables = readHTMLTable(u)
     names(tables)

     tables[[2]]
      # Print the table. Note that the values are all characters
      # not numbers. Also the column names have a preceding X since
      # R doesn't allow the variable names to start with digits.
     tmp = tables[[2]]

      # We can transform this to get the rows to be years and the columns
      # to be population counts. We'll create a matrix.
     vals = cbind(year = as.integer(gsub("X", "", names(tmp)[-1])),
                  matrix(as.integer(gsub(",", "", as.character(unlist(tmp[-1])))),
                          ncol(tmp)-1, byrow = TRUE, dimnames = list(NULL, as.character(tmp[[1]]))))

       # Let's just read the second table directly by itself.
     doc = htmlParse(u)
     tableNodes = getNodeSet(doc, "//table")
     tb = readHTMLTable(tableNodes[[2]])

      # Let's try to adapt the values on the fly.
      # We'll create a function that turns a th/td node into a val
     tryAsInteger = function(node) {
                      val = xmlValue(node)
                      ans = as.integer(gsub(",", "", val))
                      if(is.na(ans))
                          val
                      else
                          ans
                    }

     tb = readHTMLTable(tableNodes[[2]], elFun = tryAsInteger)

     tb = readHTMLTable(tableNodes[[2]], elFun = tryAsInteger,
                           colClasses = c("character", rep("integer", 9)))

[Package XML version 2.5-1 Index]