xmlEventParse              package:XML              R Documentation

_X_M_L _E_v_e_n_t/_C_a_l_l_b_a_c_k _e_l_e_m_e_n_t-_w_i_s_e _P_a_r_s_e_r

_D_e_s_c_r_i_p_t_i_o_n:

     Reads and processes the contents of an XML file or string by
     invoking user-level functions associated with different components
     of the XML tree. These include beginning and end of XML elements,
     comments, CDATA (escaped character data), entities, processing
     instructions, etc. This allows the caller to create the
     appropriate data structure from the XML document contents rather
     than the default tree (see xmlTreeParse). Functions for specific
     tags/elements can be used in addition to the  standard callback
     names.

_U_s_a_g_e:

     xmlEventParse(file, handlers=xmlHandler(), ignoreBlanks, addContext=T, useTagName=F, asText =F, trim=T, useExpat=F, isURL = F)

_A_r_g_u_m_e_n_t_s:

    file: string identifying the file that is interpreted using the
          internal expansion mechanism so it can contain \~ and other
          environment variables. As with `xmlTreeParse', if `useExpat'
          is false, this can be a URL (http or ftp) or a compressed
          file, as well as a regular local file. 

handlers: a closure object that contains  functions which will be
          invoked as the XML components in the document are encountered
          by the parser.  The standard functions are  `startElement()',
          `endElement()' `comment()', `externalEntity()',
          `entityDeclaration()', `processingInstruction', `text()'. 

ignoreBlanks: logical value indicating whether text elements made up
          entirely of white space should be included in the resulting
          `tree'. 

addContext: logical value indicating whether the callback functions  in
          `handlers' should be invoked with contextual  information
          about the parser and the position in the tree, such as node
          depth,  path indices for the node relative the root, etc. If
          this is True, each callback function  should support  .... 

useTagName: logical value indicating whether  the callback mechanism
          should look  for a function matching the tag name in the
          startElement and endElement events, before calling the
          default handler functions. This allows the caller to handle
          different element types for a particular DTD with their own
          functions directly, rather than performing a second dispatch
          in `startElement()'. 

  asText: logical value indicating that the first argument, `file', 
          should be treated as the XML text to parse, not the name of 
          a file. This allows the contents of documents to be retrieved
           from different sources (e.g. HTTP servers, XML-RPC, etc.)
          and still use this parser.

    trim: whether to strip white space from the beginning and end of
          text strings. 

useExpat: a logical value indicating whether to use the expat SAX
          parser, or to default to the libxml. If this is TRUE, the
          library must have been compiled with support for expat. See
          supportsExpat. 

   isURL: indicates whether the `file'  argument refers to a URL
          (accessible via ftp or http) or a regular file on the system.
          If `asText' is TRUE, this should not be specified. 

_D_e_t_a_i_l_s:

     This is implemented via the Expat XML parser by Jim Clark (<URL:
     http://www.jclark.com>).

_V_a_l_u_e:

     The return value is the `handlers' argument. It is assumed that
     this is a closure and that the callback functions have manipulated
     variables local to it and that the caller knows how to extract
     this.

_N_o_t_e:

     This requires the Expat XML parser to be installed.

_A_u_t_h_o_r(_s):

     Duncan Temple Lang

_R_e_f_e_r_e_n_c_e_s:

     <URL: http://www.w3.org/XML>, <URL: http://www.jclark.com/xml>

_S_e_e _A_l_s_o:

     xmlTreeParse

_E_x_a_m_p_l_e_s:

      fileName <- system.file("data", "mtcars.xml", pkg="XML")

        # Print the name of each XML tag encountered at the beginning of each
        # tag.
        # Uses the libxml SAX parser.
      xmlEventParse(fileName, list(startElement=function(name, attrs){cat(name,"\n")}), useTagName=F, addContext = F)


       # Parse the text rather than a file or URL by reading the URL's contents
       # and making it a single string. Then call xmlEventParse
     xmlURL <- "http://www.omegahat.org/Scripts/Data/mtcars.xml"
     xmlText <- paste(scan.url(xmlURL, what="",sep="\n"),"\n",collapse="\n")
     xmlEventParse(xmlText, asText=T)

