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# memoise
[](https://travis-ci.org/hadley/memoise) [](https://codecov.io/github/hadley/memoise?branch=master)
# Memoization
If a function is called multiple times with the same input, you can
often speed things up by keeping a cache of known answers that it can
retrieve. This is called memoisation <http://en.wikipedia.org/wiki/Memoization>.
The `memoise` package provides a simple syntax
```r
mf <- memoise(f)
```
to create `mf()`, a memoised wrapper around `f()`. You can clear `mf`'s
cache with
```r
forget(mf)
```
and you can test whether a function is memoised with
```r
is.memoised(mf) # TRUE
is.memoised(f) # FALSE
```
# Installation
```
devtools::install_github("hadley/memoise")
```
# External Caches
`memoise` also supports external caching in addition to the default in-memory caches.
* `cache_filesystem()` allows caching using files on a local filesystem. You
can point this to a shared file such as dropbox or google drive to share
caches between systems.
* `cache_s3()` allows caching on [Amazon S3](https://aws.amazon.com/s3/)
## AWS S3
Use `cache_s3()` to cache objects using s3 storage. Requires you to specify
a bucket using `cache_name`. When creating buckets, they must be unique among
all s3 users when created.
```r
Sys.setenv("AWS_ACCESS_KEY_ID" = "<access key>",
"AWS_SECRET_ACCESS_KEY" = "<access secret>")
mrunif <- memoise(runif, cache = cache_s3("<unique bucket name>"))
mrunif(10) # First run, saves cache
mrunif(10) # Loads cache, results should be identical
```
## Filesystem
`cache_filesystem` can be used for a file system cache. This is useful for
preserving the cache between R sessions as well as sharing between systems
when using a shared or synced files system such as Dropbox or Google Drive.
```r
fc <- cache_filesystem("~/.cache")
mrunif <- memoise(runif, cache = fc)
mrunif(20) # Results stored in local file
dbc <- cache_filesystem("~/Dropbox/.rcache")
mrunif <- memoise(runif, cache = dbc)
mrunif(20) # Results stored in Dropbox .rcache folder which will be synced between computers.
gdc <- cache_filesystem("~/Google Drive/.rcache")
mrunif <- memoise(runif, cache = gdc)
mrunif(20) # Results stored in Google Drive .rcache folder which will be synced between computers.
```
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