Log Levels concept exercise (#459)

* Log Levels concept exercise

* incorporate reviewer comments

Author: colinleach

config.json

@@ -104,6 +104,18 @@
         ],
         "status": "wip"
       },
+      {
+        "slug": "log-levels",
+        "name": "Log Levels",
+        "uuid": "6c85ef11-cd2d-4718-9f75-84c467afb2f9",
+        "concepts": [
+          "strings"
+        ],
+        "prerequisites": [
+          "vectors"
+        ],
+        "status": "wip"
+      },
       {
         "slug": "mixed-juices",
         "name": "Mixed Juices",

exercises/concept/log-levels/.docs/hints.md

@@ -0,0 +1,21 @@
+# Hints
+
+## General
+
+- Knowledge of regular expressions is not required or expected for this exercise.
+- However, students who already have regex experience are free to use it if they wish.
+
+## 1. Get message from a log line
+
+- Think about how to split the log line into useful parts.
+- You may need to remove excess whitespace.
+
+## 2. Get log level from a log line
+
+- There are various ways to pull out the desired substring, but position index may be the most basic.
+- Remember to change case.
+
+## 3. Reformat a log line
+
+- You already wrote functions to do much of the work, and using those will help you.
+- Join the pieces back together, with some extra punctuation.

exercises/concept/log-levels/.docs/instructions.md

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+# Instructions
+
+In this exercise you'll be processing log-lines.
+
+Each log line is a string formatted as follows: `"[<LEVEL>]: <MESSAGE>"`.
+
+There are three different log levels:
+
+- `INFO`
+- `WARNING`
+- `ERROR`
+
+You have three tasks, each of which will take a log line and ask you to do something with it.
+
+## 1. Get message from a log line
+
+Implement the `message` function to return a log line's message:
+
+```R
+message("[ERROR]: Invalid operation")
+#> "Invalid operation"
+```
+
+Any leading or trailing white space should be removed:
+
+```R
+message("[WARNING]:  Disk almost full\r\n")
+#> "Disk almost full"
+```
+
+## 2. Get log level from a log line
+
+Implement the `log_level` function to return a log line's log level, which should be returned in lowercase:
+
+```R
+log_level("[ERROR]: Invalid operation")
+#> "error"
+```
+
+## 3. Reformat a log line
+
+Implement the `reformat` function that reformats the log line, putting the message first and the log level after it in parentheses:
+
+```R
+reformat("[INFO]: Operation completed")
+#> "Operation completed (info)"
+```
+
+## Note
+
+Students are free to use either legacy functions from base R or the `stringr` library, and both can give short, viable solutions.