webscraping.proOften at scraping I collect images or other sequential elements into an array. Yet, afterwards I need to remove duplicate elements from an array. The magic is to make it a Set and then use Spread syntax to turn it back to array.
links = [];
$('div.items').each((index, el) => {
let link = $(el).attr('href');
links.push(link);
});
// remove repeating links
links = [...new Set(links)]See also How to remove from an array empty or undefined elements.
Often at scraping I collect images or other sequential elements into an array. Yet, afterwards I need to remove empty elements from it.
images = [];
$('div.image').each((index, el) => {
let url = $(el).attr('src');
images.push(url);
});
// remove invalid images
images = images.filter(function(img){
return img && !img.includes('undefined')
});When performing web scaping I first need to evaluate a site’s difficulty level. That is how difficult is it for the scrape procedures? Do its pages make extra XHR (Ajax) calls? Based on that I choose whether to use (1) Request scraper (eg. Cheerio) or (2) Browser automation scraper (eg. Puppeteer).
So, I’ve discovered an Apify Web Page Analyzer, a free scraper agent that analyses a target site and returns inclusive JSON data of the target web page. The presence of XHR (AJAX) helps me to decide what type of crawler to use for scraping that website.
In the post we share some basics of classification and clustering in Machine learning. We also review some of the cluster analysis methods and algorithms.
Working with generated UTF-8 files it’s a challenge to view them properly in Excel. Gladly there is a method how to properly open them in Excel.
In this post we share how to plot distribution histogram for the Weibull ditribution and the distribution of sample averages as approximated by the Normal (Gaussian) distribution. We’ll show how the approximation accuracy changes with samples volume increase.
One may get the full .ipynb file here.
Often we see “invalid data”, “clean data”, “normalize data”. What does it mean as to practical data extraction and how does one deal with that? One shot is better than 1000 words though:
Working with a Backconnect proxy service (Oxylab.io) we spent a long time looking for a way to authorize it. Originally we used JSoup to get the web pages’ content. The proxy()Â method can be used there when setting up the connection, yet it only accepts the host and port, no authentication is possible. One of the options that we found, was the following:
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function strip_tags(str){
const tags = ['a', 'em', 'div', 'span', 'p', 'i', 'button', 'img' ];
const tagsAndContent = ['picture', 'script', 'noscript', 'source'];
for(tag of tagsAndContent){
let regex = new RegExp( '<' + tag+ '.*?</' + tag + '>', 'gim');
str = str.replace( regex ,"");
}
for(tag of tags){
let regex1 = new RegExp( '<' + tag+ '.*?>', 'gim');
let regex2 = new RegExp( '</' + tag+ '>', 'gim');
str = str.replace(regex1,"").replace(regex2,"");
}
return str;
}