Html – How to read the nth line of a Parsed html in R

htmlhtml-parsingrxml-parsing

The readLines function displays all the content of the source page in one line.

con = url("target_url_here")
htmlcode = readLines(con)

readLines function has concatenated all the lines of the source page in one line. So there is no way I can navigate to the 15th line in the original html source page.

Next approach is to try parsing it using XML package or httr package.

library("httr")
html <- GET("target_url_here")
content2 = content(html,as="text")
parsedHtml = htmlParse(content2,asText=TRUE)

By printing out the parsedHtml, it retains the html format and displays all the contents as it can be seen in the source page.
Now suppose I want to extract the title, so the function

xpathSApply(parsedHtml,"//title",xmlValue)

will give the title.

But my question is, how do I navigate to any line say the 15th line of the html? In other words, how can I treat the html as a vector of strings, where each element of the vector is a separate line in the html page/parsed html object.

Best Solution

Having a better look at the docs for readLines(), it actually returns:

A character vector of length the number of lines read.

So in your case:

con = url("http://example.com/file_to_parse.html")
htmlCode = readLines(con)

you can easily do htmlCode[15] to access the 15^th line in the original html source page.

Related Solutions

Html – What are valid values for the id attribute in HTML

For HTML 4, the answer is technically:

ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods (".").

HTML 5 is even more permissive, saying only that an id must contain at least one character and may not contain any space characters.

The id attribute is case sensitive in XHTML.

As a purely practical matter, you may want to avoid certain characters. Periods, colons and '#' have special meaning in CSS selectors, so you will have to escape those characters using a backslash in CSS or a double backslash in a selector string passed to jQuery. Think about how often you will have to escape a character in your stylesheets or code before you go crazy with periods and colons in ids.

For example, the HTML declaration <div id="first.name"></div> is valid. You can select that element in CSS as #first\.name and in jQuery like so: $('#first\\.name'). But if you forget the backslash, $('#first.name'), you will have a perfectly valid selector looking for an element with id first and also having class name. This is a bug that is easy to overlook. You might be happier in the long run choosing the id first-name (a hyphen rather than a period), instead.

You can simplify your development tasks by strictly sticking to a naming convention. For example, if you limit yourself entirely to lower-case characters and always separate words with either hyphens or underscores (but not both, pick one and never use the other), then you have an easy-to-remember pattern. You will never wonder "was it firstName or FirstName?" because you will always know that you should type first_name. Prefer camel case? Then limit yourself to that, no hyphens or underscores, and always, consistently use either upper-case or lower-case for the first character, don't mix them.

A now very obscure problem was that at least one browser, Netscape 6, incorrectly treated id attribute values as case-sensitive. That meant that if you had typed id="firstName" in your HTML (lower-case 'f') and #FirstName { color: red } in your CSS (upper-case 'F'), that buggy browser would have failed to set the element's color to red. At the time of this edit, April 2015, I hope you aren't being asked to support Netscape 6. Consider this a historical footnote.

Javascript – Retrieve the position (X,Y) of an HTML element

The correct approach is to use element.getBoundingClientRect():

var rect = element.getBoundingClientRect();
console.log(rect.top, rect.right, rect.bottom, rect.left);

Internet Explorer has supported this since as long as you are likely to care about and it was finally standardized in CSSOM Views. All other browsers adopted it a long time ago.

Some browsers also return height and width properties, though this is non-standard. If you're worried about older browser compatibility, check this answer's revisions for an optimised degrading implementation.

The values returned by element.getBoundingClientRect() are relative to the viewport. If you need it relative to another element, simply subtract one rectangle from the other:

var bodyRect = document.body.getBoundingClientRect(),
    elemRect = element.getBoundingClientRect(),
    offset   = elemRect.top - bodyRect.top;

alert('Element is ' + offset + ' vertical pixels from <body>');

Best Solution

Related Solutions

Html – What are valid values for the id attribute in HTML

Javascript – Retrieve the position (X,Y) of an HTML element

Related Question