R: Load the cache database of a code chunk

load_cache {knitr} | R Documentation

## Load the cache database of a code chunk

### Description

If a code chunk has turned on the chunk option `cache = TRUE`, a cache database will be established after the document is compiled. You can use this function to manually load the database anywhere in the document (even before the code chunk). This makes it possible to use objects created later in the document earlier, e.g. in an inline R expression before the cached code chunk, which is normally not possible because knitr compiles the document in a linear fashion, and objects created later cannot be used before they are created.

### Usage

    load_cache(label, object, notfound = "NOT AVAILABLE",
        path = opts_chunk$get("cache.path"), lazy = TRUE)

### Arguments

`label` | the chunk label of the code chunk that has a cache database
`object` | the name of the object to be fetched from the database (if missing, `NULL` is returned)
`notfound` | a value to use when the `object` cannot be found
`path` | the path of the cache database (normally set in the global chunk option `cache.path`)
`lazy` | whether to `lazyLoad` the cache database (depending on the chunk option `cache.lazy = TRUE` or `FALSE` of that code chunk)

### Value

Invisible `NULL` when `object` is not specified (the cache database will be loaded as a side effect), otherwise the value of the object if found.

### Note

Apparently this function loads the value of the object from the previous run of the document, which may be problematic when the value of the object becomes different the next time the document is compiled. Normally you must compile the document twice to make sure the cache database is created, and the object can be read from it. Please use this function with caution.

### References

See the example #114 at https://github.com/yihui/knitr-examples.

[Package knitr version 1.16 Index]