158 lines
4.9 KiB
HTML
158 lines
4.9 KiB
HTML
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=yes">
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<meta name="generator" content="litedown 0.4">
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<title>Templating with knit_expand()</title>
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<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@xiee/utils@1.13.44/css/prism-xcode.min.css">
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<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@xiee/utils@1.13.44/css/default.min.css">
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</head>
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<body>
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<div class="frontmatter">
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<div class="title"><h1>Templating with knit_expand()</h1></div>
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<div class="author"><h2>Yihui Xie</h2></div>
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<div class="date"><h3>2024-11-06</h3></div>
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</div>
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<div class="body">
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<!--
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%\VignetteEngine{litedown::vignette}
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%\VignetteIndexEntry{Templating with knit_expand()}
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-->
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<p>A few simple examples:</p>
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<pre><code class="language-r">library(knitr)
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knit_expand(text = 'The value of pi is {{pi}}.')
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</code></pre>
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<pre><code>#> [1] "The value of pi is 3.14159265358979."
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</code></pre>
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<pre><code class="language-r">knit_expand(text = 'The value of a is {{a}}, so a + 1 is {{a+1}}.', a = rnorm(1))
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</code></pre>
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<pre><code>#> [1] "The value of a is 0.676489790550228, so a + 1 is 1.67648979055023."
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</code></pre>
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<pre><code class="language-r">knit_expand(text = 'The area of a circle with radius {{r}} is {{pi*r^2}}', r = 5)
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</code></pre>
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<pre><code>#> [1] "The area of a circle with radius 5 is 78.5398163397448"
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</code></pre>
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<p>Any number of variables:</p>
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<pre><code class="language-r">knit_expand(text = 'a is {{a}} and b is {{b}}, with my own pi being {{pi}} instead of {{base::pi}}', a=1, b=2, pi=3)
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</code></pre>
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<pre><code>#> [1] "a is 1 and b is 2, with my own pi being 3 instead of 3.14159265358979"
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</code></pre>
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<p>Custom delimiter <code><% %></code>:</p>
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<pre><code class="language-r">knit_expand(text = 'I do not like curly braces, so use % with <> instead: a is <% a %>.', a = 8, delim = c("<%", "%>"))
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</code></pre>
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<pre><code>#> [1] "I do not like curly braces, so use % with <> instead: a is 8."
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</code></pre>
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<p>The pyexpander delimiter:</p>
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<pre><code class="language-r">knit_expand(text = 'hello $(LETTERS[24]) and $(pi)!', delim = c("$(", ")"))
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</code></pre>
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<pre><code>#> [1] "hello X and 3.14159265358979!"
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</code></pre>
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<p>Arbitrary R code:</p>
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<pre><code class="language-r">knit_expand(text = 'you cannot see the value of x {{x=rnorm(1)}}but it is indeed created: x = {{x}}')
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</code></pre>
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<pre><code>#> [1] "you cannot see the value of x but it is indeed created: x = -0.320718473271458"
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</code></pre>
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<pre><code class="language-r">res = knit_expand(text = c(' x | x^2', '{{x=1:5;paste(sprintf("%2d | %3d", x, x^2), collapse = "\n")}}'))
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cat(res)
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</code></pre>
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<pre><code>#> x | x^2
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#> 1 | 1
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#> 2 | 4
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#> 3 | 9
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#> 4 | 16
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#> 5 | 25
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</code></pre>
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<p>The m4 example: <a href="https://en.wikipedia.org/wiki/M4_(computer_language)">https://en.wikipedia.org/wiki/M4_(computer_language)</a></p>
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<pre><code class="language-r">res = knit_expand(text = c('{{i=0;h2=function(x){i<<-i+1;sprintf("<h2>%d. %s</h2>", i, x)} }}<html>',
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'{{h2("First Section")}}', '{{h2("Second Section")}}', '{{h2("Conclusion")}}', '</html>'))
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cat(res)
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</code></pre>
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<pre><code>#> <html>
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#> <h2>1. First Section</h2>
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#> <h2>2. Second Section</h2>
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#> <h2>3. Conclusion</h2>
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#> </html>
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</code></pre>
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<p>Build regression models based on a template; loop through some variables in <code>mtcars</code>:</p>
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<pre><code class="language-r">src = lapply(names(mtcars)[2:5], function(i) {
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knit_expand(text=c("# Regression on {{i}}", '```{r lm-{{i}}}', 'lm(mpg~{{i}}, data=mtcars)', '```', ''))
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})
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# knit the source
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litedown::fuse(unlist(src), 'markdown')
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</code></pre>
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<pre><code># Regression on cyl
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``` {.r}
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lm(mpg~cyl, data=mtcars)
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```
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```
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Call:
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lm(formula = mpg ~ cyl, data = mtcars)
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Coefficients:
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(Intercept) cyl
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37.885 -2.876
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```
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# Regression on disp
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``` {.r}
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lm(mpg~disp, data=mtcars)
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```
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```
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Call:
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lm(formula = mpg ~ disp, data = mtcars)
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Coefficients:
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(Intercept) disp
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29.59985 -0.04122
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```
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# Regression on hp
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``` {.r}
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lm(mpg~hp, data=mtcars)
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```
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```
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Call:
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lm(formula = mpg ~ hp, data = mtcars)
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Coefficients:
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(Intercept) hp
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30.09886 -0.06823
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```
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# Regression on drat
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``` {.r}
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lm(mpg~drat, data=mtcars)
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```
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```
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Call:
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lm(formula = mpg ~ drat, data = mtcars)
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Coefficients:
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(Intercept) drat
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-7.525 7.678
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```
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</code></pre>
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</div>
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<script src="https://cdn.jsdelivr.net/npm/prismjs@1.29.0/components/prism-core.min.js" defer></script>
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<script src="https://cdn.jsdelivr.net/npm/prismjs@1.29.0/plugins/autoloader/prism-autoloader.min.js" defer></script>
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</body>
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</html>
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