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<!DOCTYPE html>
<html lang="" xml:lang="">
<head>
<title>stringr</title>
<meta charset="utf-8" />
<meta name="author" content="Alberto Torres Barrán" />
<meta name="date" content="2021-01-07" />
<link href="libs/remark-css-0.0.1/default.css" rel="stylesheet" />
<script src="libs/htmlwidgets-1.5.2/htmlwidgets.js"></script>
<link href="libs/str_view-0.1.0/str_view.css" rel="stylesheet" />
<script src="libs/str_view-binding-1.4.0/str_view.js"></script>
<link rel="stylesheet" href="custom.css" type="text/css" />
</head>
<body>
<textarea id="source">
class: center, middle, inverse, title-slide
# stringr
## Entornos de Análisis de Datos: R
### Alberto Torres Barrán
### 2021-01-07
---
<script type="text/x-mathjax-config">
MathJax.Hub.Config({
TeX: {
Macros: {
Xcal: "{\\mathcal{X}}",
Xbf: "{\\mathbf{X}}",
Qbf: "{\\mathbf{Q}}",
Zbf: "{\\mathbf{Z}}",
Vbf: "{\\mathbf{V}}",
Hbf: "{\\mathbf{H}}",
Rbb: "{\\mathbb{R}}"
},
extensions: ["AMSmath.js","AMSsymbols.js"]
}
});
</script>
## Expresiones regulares
- Lenguaje que describe patrones en cadenas de caracteres
- La mayoría de lenguajes de programación implementan expresiones regulares
- La sintaxis difiere ligeramente
- [Expresiones regulares en R](https://stat.ethz.ch/R-manual/R-devel/library/base/html/regex.html)
- [*Vignette* expresiones regulares](https://cran.r-project.org/web/packages/stringr/vignettes/regular-expressions.html)
---
## Ejemplos
```r
x <- c("moto", "coche", "autobus")
str_view(x, "co")
```
<div id="htmlwidget-9b6ee66a23cbaddc89d0" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-9b6ee66a23cbaddc89d0">{"x":{"html":"<ul>\n <li>moto<\/li>\n <li><span class='match'>co<\/span>che<\/li>\n <li>autobus<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
---
```r
str_view(x, ".o")
```
<div id="htmlwidget-6f3000e3320b57672875" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-6f3000e3320b57672875">{"x":{"html":"<ul>\n <li><span class='match'>mo<\/span>to<\/li>\n <li><span class='match'>co<\/span>che<\/li>\n <li>au<span class='match'>to<\/span>bus<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
---
```r
str_view_all(x, ".o")
```
<div id="htmlwidget-dc1c40884684056068e7" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-dc1c40884684056068e7">{"x":{"html":"<ul>\n <li><span class='match'>mo<\/span><span class='match'>to<\/span><\/li>\n <li><span class='match'>co<\/span>che<\/li>\n <li>au<span class='match'>to<\/span>bus<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
---
## Caracteres especiales
- El `.` es un carácter especial de las expresiones regulares que concuerda con todos
- ¿Como podemos concordar con el carácter `"."`?
- Hay que "escapar" el `.` en la expresión regular con la barra invertida `"\"`
- Las expresiones regulares se representan con cadenas de caracteres:
* la barra invertida también es un carácter especial de las cadenas de caracteres
* tenemos que escapar la barra invertida con otra barra invertida
```r
writeLines("\\.")
## \.
```
```r
str_view(c("hola.", "adios."), "a\\.")
```
<div id="htmlwidget-8ff2931db926743befdc" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-8ff2931db926743befdc">{"x":{"html":"<ul>\n <li>hol<span class='match'>a.<\/span><\/li>\n <li>adios.<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
<!--
```r
writeLines("\\\\")
## \\
```
```r
str_view("carpeta\\fichero", "\\\\")
```
<div id="htmlwidget-83ff778cee7c30794bb1" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-83ff778cee7c30794bb1">{"x":{"html":"<ul>\n <li>carpeta<span class='match'>\\<\/span>fichero<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
-->
---
## Anclas
`^` representa el inicio de la cadena y `$` representa el final
```r
str_view(c("tapar", "destapar"), "^tapar")
```
<div id="htmlwidget-8f9de6abc0467d4f0838" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-8f9de6abc0467d4f0838">{"x":{"html":"<ul>\n <li><span class='match'>tapar<\/span><\/li>\n <li>destapar<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
---
## Clases de caracteres
* Listas de caracteres. Se concuerda con cualquier carácter de la lista:
- `[abc]`: a, b, o c
- `[^abc]`: cualquier cosa excepto a, b, o c
- `ab|cd`: "ab" o "cd", pero no "abd" ni "acd"
* Listas de caracteres predefinidas:
- `[:alpha:]`, caracteres del alfabeto, `[A-z]`
- `[:alnum:]`, caracteres alfanuméricos
- `\\d` o `[:digit:]`: cualquier dígito
- `\\s` o `[:space:]`: espacios, tabulación, saltos de línea y retorno de carro
---
## Repetición
.col-left[
- `?`: 0 o 1 vez
- `+`: 1 o más
- `*`: 0 o más
- `{n}`: exactamente n veces
- `{n,}`: n veces o más
- `{,m}`: como mucho m veces
- `{n,m}`: entre n y m veces
]
.col-right[
```r
n <- c("4.5", "6", ".5", "5.", "a", "4.a")
str_view(n, "^\\d+\\.?\\d*$")
```
<div id="htmlwidget-dc9af7d2a4d39e6e4bfd" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-dc9af7d2a4d39e6e4bfd">{"x":{"html":"<ul>\n <li><span class='match'>4.5<\/span><\/li>\n <li><span class='match'>6<\/span><\/li>\n <li>.5<\/li>\n <li><span class='match'>5.<\/span><\/li>\n <li>a<\/li>\n <li>4.a<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
]
---
## Ejemplos
```r
str_view(c("test@test.com", "test@test12.com", "test@test",
"test@test.es", "@test.com", "te st@test.com", "test@test.com hola"),
".+@[^\\d\\s]+\\.(com|es)")
```
<div id="htmlwidget-144987711e066fc9c892" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-144987711e066fc9c892">{"x":{"html":"<ul>\n <li><span class='match'>test@test.com<\/span><\/li>\n <li>test@test12.com<\/li>\n <li>test@test<\/li>\n <li><span class='match'>test@test.es<\/span><\/li>\n <li>@test.com<\/li>\n <li><span class='match'>te st@test.com<\/span><\/li>\n <li><span class='match'>test@test.com<\/span> hola<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
---
```r
str_view(c("test@test.com", "test@test12.com", "test@test",
"test@test.es", "@test.com", "te st@test.com", "test@test.com hola"),
".+@[^\\d\\s]+\\.(com|es)$")
```
<div id="htmlwidget-95aee346d43f342369b7" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-95aee346d43f342369b7">{"x":{"html":"<ul>\n <li><span class='match'>test@test.com<\/span><\/li>\n <li>test@test12.com<\/li>\n <li>test@test<\/li>\n <li><span class='match'>test@test.es<\/span><\/li>\n <li>@test.com<\/li>\n <li><span class='match'>te st@test.com<\/span><\/li>\n <li>test@test.com hola<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
---
```r
str_view(c("981945678", "981 945678", "+34 981945678"),
"(\\+34\\s)?\\d{9}")
```
<div id="htmlwidget-14ae3a310ca9244814e4" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-14ae3a310ca9244814e4">{"x":{"html":"<ul>\n <li><span class='match'>981945678<\/span><\/li>\n <li>981 945678<\/li>\n <li><span class='match'>+34 981945678<\/span><\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
---
```r
str_view(c("981945678", "981 945678", "+34 981945678", "981 94 56 78"),
"(\\+34\\s)?\\d{3}\\s?\\d{6}")
```
<div id="htmlwidget-5373a7f35e8b779806fe" style="width:960px;height:100%;" class="str_view html-widget"></div>
<script type="application/json" data-for="htmlwidget-5373a7f35e8b779806fe">{"x":{"html":"<ul>\n <li><span class='match'>981945678<\/span><\/li>\n <li><span class='match'>981 945678<\/span><\/li>\n <li><span class='match'>+34 981945678<\/span><\/li>\n <li>981 94 56 78<\/li>\n<\/ul>"},"evals":[],"jsHooks":[]}</script>
---
## Cadenas de caracteres
- Las cadenas de caracteres se crean con comillas dobles `""` o simples `''`
- La `\` se usa para escapar ciertos caracteres especiales: `"\""`, `"\\"`, `"\n"`, etc.
---
## Librería stringr
- Implementa muchas operaciones con cadenas de caracteres
- Todas las funciones comienzan con el prefijo común `str_`
- Muchas de ellas tienen como entrada las expresiones regulares que vimos anteriormente
---
## Operaciones básicas con cadenas
- Longitud
```r
str_length(c("hola", "alberto", NA))
## [1] 4 7 NA
```
- Concatenar cadenas
```r
str_c("a", "b", "c")
## [1] "abc"
```
```r
str_c("a", "b", "c", sep = ", ")
## [1] "a, b, c"
```
```r
str_c("pre-", c("a", "b", "c"), "-suf")
## [1] "pre-a-suf" "pre-b-suf" "pre-c-suf"
```
---
## Indexando cadenas
- Se puede obtener una subcadena a partir de las posiciones
```r
str_sub("hola", 2, 3)
## [1] "ol"
```
- También se puede modificar si le asignamos un nuevo valor
```r
x <- c("hola", "que", "tal")
str_sub(x, 2, 4) <- str_to_upper(str_sub(x, 2, 4))
x
## [1] "hOLA" "qUE" "tAL"
```
---
## Operaciones con expresiones regulares
- `str_detect()` devuelve un vector lógico indicando si la expresión regular concuerda con la cadena o no
```r
str_detect(c("aba", "ebf", "atp"), "^a")
## [1] TRUE FALSE TRUE
```
- `str_count()` devuelve **cuántas** concordancias hay en cada cadena
```r
str_count(c("aba", "ebf", "atp"), "a")
## [1] 2 0 1
```
---
## Extraer concordancias
- `str_extract()`: extrae la parte de la cadena que concuerda con la expresión regular (únicamente la primera concordancia)
```r
str_extract(c("ab (cd)", "ef (gh)", "ij (kl)"), "\\(.*\\)")
## [1] "(cd)" "(gh)" "(kl)"
```
- `str_extract_all()`: devuelve todas las concordancias
```r
str_extract_all(c("a b c", "a f g"), "[abc]")
## [[1]]
## [1] "a" "b" "c"
##
## [[2]]
## [1] "a"
```
---
## Reemplazar concordancias
- `str_replace()`: reemplaza la primera concordancia por otra cadena de texto
```r
x <- c("coche", "moto", "autobus")
str_replace(x, "[aeiou]", "-")
## [1] "c-che" "m-to" "-utobus"
```
- `str_replace_all()`: reemplaza **todas** las concordancias
```r
str_replace_all(x, "[aeiou]", "-")
## [1] "c-ch-" "m-t-" "--t-b-s"
```
---
## Dividir una cadena
- `str_split()` divide una cadena de acuerdo con una expresión regular
```r
str_split(c("a b c", "a f g"), "\\s")
## [[1]]
## [1] "a" "b" "c"
##
## [[2]]
## [1] "a" "f" "g"
```
- `str_split_fixed()` es una variante donde se especifica exactamente cuantas partes se devuelven
```r
str_split_fixed(c("a b c", "a f g"), "\\s", n = 3)
## [,1] [,2] [,3]
## [1,] "a" "b" "c"
## [2,] "a" "f" "g"
```
- `tidyr::separate()` realiza esta misma operación sobre las columnas de un data frame, acepta expresiones regulares
</textarea>
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