[rust] ETL

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diff --git a/rust/etl/.exercism/metadata.json b/rust/etl/.exercism/metadata.json
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+{"track":"rust","exercise":"etl","id":"c78c2dc057e14376b48708b6e603c67d","url":"https://exercism.io/my/solutions/c78c2dc057e14376b48708b6e603c67d","handle":"dyamon","is_requester":true,"auto_approve":false}
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diff --git a/rust/etl/.gitignore b/rust/etl/.gitignore
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+# Generated by Cargo
+# will have compiled files and executables
+/target/
+**/*.rs.bk
+
+# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
+# More information here http://doc.crates.io/guide.html#cargotoml-vs-cargolock
+Cargo.lock
diff --git a/rust/etl/Cargo.toml b/rust/etl/Cargo.toml
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+++ b/rust/etl/Cargo.toml
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+[package]
+edition = "2018"
+name = "etl"
+version = "1.0.0"
diff --git a/rust/etl/README.md b/rust/etl/README.md
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+# ETL
+
+We are going to do the `Transform` step of an Extract-Transform-Load.
+
+### ETL
+
+Extract-Transform-Load (ETL) is a fancy way of saying, "We have some crufty, legacy data over in this system, and now we need it in this shiny new system over here, so
+we're going to migrate this."
+
+(Typically, this is followed by, "We're only going to need to run this
+once." That's then typically followed by much forehead slapping and
+moaning about how stupid we could possibly be.)
+
+### The goal
+
+We're going to extract some Scrabble scores from a legacy system.
+
+The old system stored a list of letters per score:
+
+- 1 point: "A", "E", "I", "O", "U", "L", "N", "R", "S", "T",
+- 2 points: "D", "G",
+- 3 points: "B", "C", "M", "P",
+- 4 points: "F", "H", "V", "W", "Y",
+- 5 points: "K",
+- 8 points: "J", "X",
+- 10 points: "Q", "Z",
+
+The shiny new Scrabble system instead stores the score per letter, which
+makes it much faster and easier to calculate the score for a word. It
+also stores the letters in lower-case regardless of the case of the
+input letters:
+
+- "a" is worth 1 point.
+- "b" is worth 3 points.
+- "c" is worth 3 points.
+- "d" is worth 2 points.
+- Etc.
+
+Your mission, should you choose to accept it, is to transform the legacy data
+format to the shiny new format.
+
+### Notes
+
+A final note about scoring, Scrabble is played around the world in a
+variety of languages, each with its own unique scoring table. For
+example, an "E" is scored at 2 in the Māori-language version of the
+game while being scored at 4 in the Hawaiian-language version.
+
+## Rust Installation
+
+Refer to the [exercism help page][help-page] for Rust installation and learning
+resources.
+
+## Writing the Code
+
+Execute the tests with:
+
+```bash
+$ cargo test
+```
+
+All but the first test have been ignored. After you get the first test to
+pass, open the tests source file which is located in the `tests` directory
+and remove the `#[ignore]` flag from the next test and get the tests to pass
+again. Each separate test is a function with `#[test]` flag above it.
+Continue, until you pass every test.
+
+If you wish to run all ignored tests without editing the tests source file, use:
+
+```bash
+$ cargo test -- --ignored
+```
+
+To run a specific test, for example `some_test`, you can use:
+
+```bash
+$ cargo test some_test
+```
+
+If the specific test is ignored use:
+
+```bash
+$ cargo test some_test -- --ignored
+```
+
+To learn more about Rust tests refer to the [online test documentation][rust-tests]
+
+Make sure to read the [Modules][modules] chapter if you
+haven't already, it will help you with organizing your files.
+
+## Further improvements
+
+After you have solved the exercise, please consider using the additional utilities, described in the [installation guide](https://exercism.io/tracks/rust/installation), to further refine your final solution.
+
+To format your solution, inside the solution directory use
+
+```bash
+cargo fmt
+```
+
+To see, if your solution contains some common ineffective use cases, inside the solution directory use
+
+```bash
+cargo clippy --all-targets
+```
+
+## Submitting the solution
+
+Generally you should submit all files in which you implemented your solution (`src/lib.rs` in most cases). If you are using any external crates, please consider submitting the `Cargo.toml` file. This will make the review process faster and clearer.
+
+## Feedback, Issues, Pull Requests
+
+The [exercism/rust](https://github.com/exercism/rust) repository on GitHub is the home for all of the Rust exercises. If you have feedback about an exercise, or want to help implement new exercises, head over there and create an issue. Members of the rust track team are happy to help!
+
+If you want to know more about Exercism, take a look at the [contribution guide](https://github.com/exercism/docs/blob/master/contributing-to-language-tracks/README.md).
+
+[help-page]: https://exercism.io/tracks/rust/learning
+[modules]: https://doc.rust-lang.org/book/ch07-02-defining-modules-to-control-scope-and-privacy.html
+[cargo]: https://doc.rust-lang.org/book/ch14-00-more-about-cargo.html
+[rust-tests]: https://doc.rust-lang.org/book/ch11-02-running-tests.html
+
+## Source
+
+The Jumpstart Lab team [http://jumpstartlab.com](http://jumpstartlab.com)
+
+## Submitting Incomplete Solutions
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.
diff --git a/rust/etl/src/lib.rs b/rust/etl/src/lib.rs
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+++ b/rust/etl/src/lib.rs
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+use std::collections::BTreeMap;
+
+pub fn transform(h: &BTreeMap<i32, Vec<char>>) -> BTreeMap<char, i32> {
+    h.iter()
+        .flat_map(|(k, v)| v.iter().map(move |x| (x.to_ascii_lowercase(), *k)))
+        .collect()
+}
diff --git a/rust/etl/tests/etl.rs b/rust/etl/tests/etl.rs
new file mode 100644
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+++ b/rust/etl/tests/etl.rs
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+use std::collections::BTreeMap;
+
+#[test]
+fn test_transform_one_value() {
+    let input = input_from(&[(1, vec!['A'])]);
+
+    let expected = expected_from(&[('a', 1)]);
+
+    assert_eq!(expected, etl::transform(&input));
+}
+
+#[test]
+fn test_transform_more_values() {
+    let input = input_from(&[(1, vec!['A', 'E', 'I', 'O', 'U'])]);
+
+    let expected = expected_from(&[('a', 1), ('e', 1), ('i', 1), ('o', 1), ('u', 1)]);
+
+    assert_eq!(expected, etl::transform(&input));
+}
+
+#[test]
+fn test_more_keys() {
+    let input = input_from(&[(1, vec!['A', 'E']), (2, vec!['D', 'G'])]);
+
+    let expected = expected_from(&[('a', 1), ('e', 1), ('d', 2), ('g', 2)]);
+
+    assert_eq!(expected, etl::transform(&input));
+}
+
+#[test]
+fn test_full_dataset() {
+    let input = input_from(&[
+        (1, vec!['A', 'E', 'I', 'O', 'U', 'L', 'N', 'R', 'S', 'T']),
+        (2, vec!['D', 'G']),
+        (3, vec!['B', 'C', 'M', 'P']),
+        (4, vec!['F', 'H', 'V', 'W', 'Y']),
+        (5, vec!['K']),
+        (8, vec!['J', 'X']),
+        (10, vec!['Q', 'Z']),
+    ]);
+
+    let expected = expected_from(&[
+        ('a', 1),
+        ('b', 3),
+        ('c', 3),
+        ('d', 2),
+        ('e', 1),
+        ('f', 4),
+        ('g', 2),
+        ('h', 4),
+        ('i', 1),
+        ('j', 8),
+        ('k', 5),
+        ('l', 1),
+        ('m', 3),
+        ('n', 1),
+        ('o', 1),
+        ('p', 3),
+        ('q', 10),
+        ('r', 1),
+        ('s', 1),
+        ('t', 1),
+        ('u', 1),
+        ('v', 4),
+        ('w', 4),
+        ('x', 8),
+        ('y', 4),
+        ('z', 10),
+    ]);
+
+    assert_eq!(expected, etl::transform(&input));
+}
+
+fn input_from(v: &[(i32, Vec<char>)]) -> BTreeMap<i32, Vec<char>> {
+    v.iter().cloned().collect()
+}
+
+fn expected_from(v: &[(char, i32)]) -> BTreeMap<char, i32> {
+    v.iter().cloned().collect()
+}