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class: center, middle, title

# UE Visualisation

### 2020-2021

## Dr. Maxime Wack

### AHU Informatique médicale
#### Hôpital Européen Georges Pompidou, &lt;/br&gt; Université de Paris

---

# Web scraping

### Utilisation de `httr` et `rvest`

## httr

Permet de faire des requêtes réseau

→ interroger et télécharger directement depuis R

## rvest

Extraction de données depuis des pages HTML

---

# httr


Télécharger une page wikipedia


```r
GET("https://en.wikipedia.org/wiki/Comparison_of_operating_systems") -&gt; wiki
```


```
## Response [https://en.wikipedia.org/wiki/Comparison_of_operating_systems]
##   Date: 2020-11-17 03:43
##   Status: 200
##   Content-Type: text/html; charset=UTF-8
##   Size: 227 kB
## &lt;!DOCTYPE html&gt;
## &lt;html class="client-nojs" lang="en" dir="ltr"&gt;
## &lt;head&gt;
## &lt;meta charset="UTF-8"/&gt;
## &lt;title&gt;Comparison of operating systems - Wikipedia&lt;/title&gt;
## &lt;script&gt;document.documentElement.className="client-js";RLCONF={"wgBreakFrames...
## "Articles with unsourced statements from February 2007","Wikipedia articles n...
## "Q3345986"};RLSTATE={"ext.globalCssJs.user.styles":"ready","site.styles":"rea...
## "ext.wikimediaEvents","ext.navigationTiming","ext.uls.compactlinks","ext.uls....
## &lt;script&gt;(RLQ=window.RLQ||[]).push(function(){mw.loader.implement("user.option...
## ...
```

---

# Parsing HTML


```r
wiki %&gt;%
  read_html -&gt; wiki_html
```


```
## {html_document}
## &lt;html class="client-nojs" lang="en" dir="ltr"&gt;
## [1] &lt;head&gt;\n&lt;meta http-equiv="Content-Type" content="text/html; charset=UTF-8 ...
## [2] &lt;body class="mediawiki ltr sitedir-ltr mw-hide-empty-elt ns-0 ns-subject  ...
```

---

# Sélecteurs CSS

[W3Schools](https://www.w3schools.com/cssref/css_selectors.asp)

### Selecteurs permettant d'identifier un **nœud** précis dans le **DOM** (Document Object Model) d'une page HTML

### Permet de sélectionner par identifiant, classe, position dans la hiérarchie, position entre élements d'un même niveau, ou relativement entre élements

### Utiliser l'**inspecteur** des outils de développement du navigateur pour identifier les éléments à capturer

---

# Sélecteurs CSS


```r
wiki_html %&gt;%
  html_nodes(".wikitable")
```

```
## {xml_nodeset (4)}
## [1] &lt;table class="wikitable sortable" style="font-size: smaller; text-align:  ...
## [2] &lt;table class="wikitable sortable" style="font-size: smaller; text-align:  ...
## [3] &lt;table class="wikitable" style="font-size: smaller; text-align: center; w ...
## [4] &lt;table class="wikitable" style="font-size: smaller; text-align: center; w ...
```


```r
wiki_html %&gt;%
  html_node("div + .wikitable")
```

```
## {html_node}
## &lt;table class="wikitable sortable" style="font-size: smaller; text-align: center; width: auto; sortby: name;"&gt;
## [1] &lt;tbody&gt;\n&lt;tr&gt;\n&lt;th&gt;Name\n&lt;/th&gt;\n&lt;th&gt;Creator\n&lt;/th&gt;\n&lt;th abbr="Initial rel ...
```

---

# Extraction d'une table


```r
wiki_html %&gt;%
  html_node("div + .wikitable") %&gt;%
  html_table -&gt; wikitable
```

<div id="htmlwidget-bb3e3440d2054f364517" style="width:100%;height:auto;" class="datatables html-widget"></div>
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US$19.99 on the Mac App Store","Discontinued; Was bundled with HP-3000 CISC hardware \"Classic\"","Bundled with hardware","Discontinued; Was bundled with HP-3000 PA-RISC hardware","Free","Free","Superseded by Novell Open Enterprise Server; Was US$184 (equivalent to $219.28 in 2019) (one-user)","Discontinued; Was bundled with hardware, then sold separately","Free","Free","Commercial, free non-commercial use","Bundled with hardware","Bundled with hardware","Bundled with hardware","Discontinued (see ArcaOS successor); Was US$300 (equivalent to $433.17 in 2019)","Free","Bundled with BlackBerry 10 and PlayBook devices. 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---

# Exercices

### Transformer cette table en forme normale

### Extraire la table avec les informations techniques

### Identifier les OS libres fonctionnant avec un microkernel
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