New translations cache.md (Japanese)

locale/ja/episodes/cache.Rmd

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+---
+title: Loading Workflow Objects
+teaching: 10
+exercises: 2
+---
+
+```{r}
+#| label: setup
+#| echo: FALSE
+#| message: FALSE
+#| warning: FALSE
+library(targets)
+source("files/lesson_functions.R")
+```
+
+:::::::::::::::::::::::::::::::::::::: questions
+
+- ワークフローはどこで行われるのか？
+- ワークフローによって構築されたオブジェクトを確認するには？
+
+::::::::::::::::::::::::::::::::::::::::::::::::
+
+::::::::::::::::::::::::::::::::::::: objectives
+
+- Explain where `targets` runs the workflow and why
+- Be able to load objects built by the workflow into your R session
+
+::::::::::::::::::::::::::::::::::::::::::::::::
+
+::::::::::::::::::::::::::::::::::::: instructor
+
+Episode summary: Show how to get at the objects that we built
+
+:::::::::::::::::::::::::::::::::::::
+
+## ワークフローはどこで行われるのか？
+
+So we just finished running our first workflow.
+Now you probably want to look at its output.
+But, if we just call the name of the object (for example, `penguins_data`), we get an error.
+
+```{r}
+#| label: error
+penguins_data
+```
+
+Where are the results of our workflow?
+
+::::::::::::::::::::::::::::::::::::: instructor
+
+- To reinforce the concept of `targets` running in a separate R session, you may want to pretend trying to run `penguins_data`, then feigning surprise when it doesn't work and using it as a teaching moment (errors are pedagogy!).
+
+::::::::::::::::::::::::::::::::::::::::::::::::
+
+We don't see the workflow results because `targets` **runs the workflow in a separate R session** that we can't interact with.
+This is for reproducibility---the objects built by the workflow should only depend on the code in your project, not any commands you may have interactively given to R.
+
+Fortunately, `targets` has two functions that can be used to load objects built by the workflow into our current session, `tar_load()` and `tar_read()`.
+Let's see how these work.
+
+## tar\_load()
+
+`tar_load()` loads an object built by the workflow into the current session.
+Its first argument is the name of the object you want to load.
+Let's use this to load `penguins_data` and get an overview of the data with `summary()`.
+
+```{r}
+#| label: targets-run-hide
+#| echo: FALSE
+# When building the Rmd, each instance of the workflow is isolated, so need
+# to re-run
+plan_1_dir <- make_tempdir()
+pushd(plan_1_dir)
+write_example_plan("plan_1.R")
+tar_make(reporter = "silent")
+penguins_csv_file_hide <- tar_read(penguins_csv_file)
+penguins_data_hide <- tar_read(penguins_data)
+popd()
+```
+
+```{r}
+#| label: targets-load
+#| echo: [2, 3]
+pushd(plan_1_dir)
+tar_load(penguins_data)
+summary(penguins_data)
+popd()
+```
+
+`tar_load()`は、その**副作用**、つまり、目的のオブジェクトを現在のRセッションにロードするために使用されることに注意してください。
+It doesn't actually return a value.
+
+## tar\_read()
+
+`tar_read()` is similar to `tar_load()` in that it is used to retrieve objects built by the workflow, but unlike `tar_load()`, it returns them directly as output.
+
+Let's try it with `penguins_csv_file`.
+
+```{r}
+#| label: targets-read-show
+#| echo: [2]
+pushd(plan_1_dir)
+tar_read(penguins_csv_file)
+popd()
+```
+
+We immediately see the contents of `penguins_csv_file`.
+But it has not been loaded into the environment.
+If you try to run `penguins_csv_file` now, you will get an error:
+
+```{r}
+#| label: error-2
+penguins_csv_file
+```
+
+## When to use which function
+
+`tar_load()` tends to be more useful when you want to load objects and do things with them.
+`tar_read()` is more useful when you just want to immediately inspect an object.
+
+## The targets cache
+
+If you close your R session, then re-start it and use `tar_load()` or `tar_read()`, you will notice that it can still load the workflow objects.
+In other words, the workflow output is **saved across R sessions**.
+How is this possible?
+
+You may have noticed a new folder has appeared in your project, called `_targets`.
+This is the **targets cache**.
+It contains all of the workflow output; that is how we can load the targets built by the workflow even after quitting then restarting R.
+
+**You should not edit the contents of the cache by hand** (with one exception).
+Doing so would make your analysis non-reproducible.
+
+The one exception to this rule is a special subfolder called `_targets/user`.
+This folder does not exist by default.
+You can create it if you want, and put whatever you want inside.
+
+Generally, `_targets/user` is a good place to store files that are not code, like data and output.
+
+Note that if you don't have anything in `_targets/user` that you need to keep around, it is possible to "reset" your workflow by simply deleting the entire `_targets` folder. Of course, this means you will need to run everything over again, so don't do this lightly!
+
+::::::::::::::::::::::::::::::::::::: keypoints
+
+- `targets` workflows are run in a separate, non-interactive R session
+- `tar_load()` loads a workflow object into the current R session
+- `tar_read()` reads a workflow object and returns its value
+- The `_targets` folder is the cache and generally should not be edited by hand
+
+::::::::::::::::::::::::::::::::::::::::::::::::