CODEWITHSUNDEEP
regexr
jrara
jrara

Reputation: 17021

How to parse html string using R?

How to grep data item from this html string

a <- "<div class=\"tst-10\">100%</div>"

so that the result is 100%? The main idea is to get data between > <.

Upvotes: 3

Views: 1273

Answers (2)

Sacha Epskamp
Sacha Epskamp

Reputation: 47642

I always use this regular expression to remove HTML tags:

gsub("<(.|\n)*?>","",a)

Gives:

[1] "100%"

Differs from mrdwab's in that I just remove every html tag and his extracts content from within html tags, which is probably more appropriate for this example. Look out that both will give different results if there are more tags:

> gsub("(<.*>)(.*)(<.*>)", "\\2", paste(a,"<lalala>foo</lalala>"))
[1] "foo"

> gsub("<(.|\n)*?>","", paste(a,"<lalala>foo</lalala>"))
[1] "100% foo"

I think that I found it here on SO once, not sure which answer.

Upvotes: 4

A5C1D2H2I1M1N2O1R2T1
A5C1D2H2I1M1N2O1R2T1

Reputation: 193687

I would use gsub() in this case:

gsub("(<.*>)(.*)(<.*>)", "\\2", a)
[1] "100%"

Basically, this breaks the string up into three parts, each separated by regular brackets ( and ). We can then use these as backreferences. The contents matched by the first set of backreferences can be referred to as \1 (use a double slash to escape the special character), those matched in the second, \2 and so on.

So, essentially, we're saying parse this string, figure out what matches my conditions, and return only the second backreference.

Piece by piece:

  • <.*> says to look for a "<" followed by any number of any characters ".*" up until you get to a ">"
  • .* means to match any number of characters (up until the next condition)

Keeping this in mind, you could actually probably use gsub("(.*>)(.*)(<.*)", "\\2", a) and get the same result.

Upvotes: 5

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