28.30 Selective Lines of Code
REVIEW Another useful formatting trick is to include only the top few and bottom few lines of a block of code. We can again do this using hooks. This time it is through a source hook.
$set(src.top=NULL)
opts_chunk$set(src.bot=NULL)
opts_chunk$set(source=function(x, options)
knit_hooks
{# Split string into separate lines.
<- unlist(stringr::str_split(x, "\n"))
x # Trim to the number of lines specified.
if (!is.null(n <- options$src.top))
{if (length(x) > n)
{# Truncate the output.
if (is.null(m <-options$src.bot)) m <- 0
<- c(head(x, n+1), "\n....\n", tail(x, m+2))
x
}
}# Paste lines back together.
<- paste(x, collapse="\n")
x hook_source(x, options)
})
Now we repaet this code chunk in the source of this current document,
but we set src.top=4
and src.bot=4
:
$set(src.top=NULL)
opts_chunk$set(src.bot=NULL)
opts_chunk$set(source=function(x, options)
knit_hooks
{# Split string into separate lines.
....
}}
# Paste lines back together.
<- paste(x, collapse="\n")
x hook_source(x, options)
})
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