bird-watcher concept exercise

config.json

@@ -66,6 +66,18 @@
         "prerequisites": [],
         "status": "wip"
       },
+      {
+        "slug": "bird-watcher",
+        "name": "Bird Watcher",
+        "uuid": "ceac4ca0-3bfe-4ca7-9b83-3c9d465ef67f",
+        "concepts": [
+          "vector-filtering"
+        ],
+        "prerequisites": [
+          "vectors"
+        ],
+        "status": "wip"
+      },
       {
         "slug": "cars-assemble",
         "name": "Cars, Assemble",

exercises/concept/bird-watcher/.docs/hints.md

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+# Hints

exercises/concept/bird-watcher/.docs/instructions.md

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+# Instructions
+
+You're an avid bird watcher that keeps track of how many birds have visited your garden in the last seven days.
+
+You have six tasks, all dealing with the numbers of birds that visited your garden.
+
+## 1. Check how many birds visited today
+
+Implement the `today()` function to return how many birds visited your garden today. The bird counts are ordered by day, with the first element being the count of the oldest day, and the last element being today's count.
+
+```R
+birds_per_day <- c(2, 5, 0, 7, 4, 1)
+today(birds_per_day)
+# => 1
+```
+
+## 2. Increment today's count
+
+Implement the `increment_todays_count()` function to increment today's count:
+
+```R
+birds_per_day <- c(2, 5, 0, 7, 4, 1)
+increment_todays_count(birds_per_day)
+# => c(2, 5, 0, 7, 4, 2)
+```
+
+## 3. Check if there was a day with no visiting birds
+
+Implement the `has_day_without_birds()` function that returns `TRUE` if there was a day at which zero birds visited the garden; otherwise, return `FALSE`:
+
+```R
+birds_per_day <- c(2, 5, 0, 7, 4, 1)
+has_day_without_birds(birds_per_day)
+# => true
+```
+
+## 4. Calculate the number of visiting birds for the first number of days
+
+Implement the `count_for_first_days()` function that returns the number of birds that have visited your garden from the start of the week, but limit the count to the specified number of days from the start of the week.
+
+```R
+birds_per_day <- c(2, 5, 0, 7, 4, 1)
+count_for_first_days(birds_per_day, 4)
+# => 14
+```
+
+## 5. Calculate the number of busy days
+
+Some days are busier that others. A busy day is one where five or more birds have visited your garden.
+Implement the `busy_days()` function to return the number of busy days:
+
+```R
+birds_per_day <- c(2, 5, 0, 7, 4, 1)
+busy_days(birds_per_day)
+# => 2
+```

exercises/concept/bird-watcher/.docs/introduction.md

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+# Introduction
+
+We saw in the `vectors` concept that a vector can be used in a conditional expression, giving a vector of booleans. This in turn can be used in functions such as `all()` and `any()`.
+
+```R
+> v <- c(4, 7, 10)
+> v >= 6
+[1] FALSE  TRUE  TRUE
+> all(v > 6)
+[1] FALSE    # not all elements match this condition
+> any(v > 6)
+[1] TRUE     # at least one element matches
+```
+
+The technique is much more powerful than this.
+
+## Array subsets
+
+Selected elements of an array can be pulled out with an index number or a vector of indices:
+
+```R
+> v <- 5:10
+> v
+[1]  5  6  7  8  9 10
+> v[3] 
+[1] 7
+> v[c(2, 4)]
+[1] 6 8
+```
+
+Alternatively, use a vector of booleans to filter the original vector, returning a subset of entries matched to a `TRUE` value:
+
+```R
+> v <- 1:3
+> bools <- c(FALSE, TRUE, TRUE)
+> v[bools]
+[1] 2 3
+```
+
+It is a small step from there to generating the boolean vector with a conditional expression:
+
+```R
+> v[v >= 2]
+[1] 2 3
+```

exercises/concept/bird-watcher/.meta/config.json

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+{
+  "authors": ["colinleach"],
+  "contributors": [],
+  "files": {
+    "solution": ["bird-watcher.R"],
+    "test": ["test_bird-watcher.R"],
+    "exemplar": [".meta/exemplar.R"]
+  },
+  "forked_from": ["Csharp/bird-watcher"],
+  "blurb": "Learn about R vectors by keeping track of how many birds visit your garden."
+}

exercises/concept/bird-watcher/.meta/design.md

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+# Design
+
+## Goal
+
+The goal of this exercise is to build on the `vectors` concept by teaching the student more about vector filtering/subsetting in R. It is the second exercise on this concept, after `elyses-analytic-enchantments`.
+
+## Learning objectives
+
+- Practice the use of conditional expressions to get a subset of the original vector.
+
+## Out of scope
+
+- Recycling is not mentioned within this exercise, though it is explained in `vector-filtering/about.md` which unlocks on completing this exercise.
+
+## Concepts
+
+The Concepts this exercise unlocks are:
+
+- `vector-functions`
+- `nothingness`
+
+## Prerequisites
+
+- `vectors`

exercises/concept/bird-watcher/.meta/exemplar.R

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+today <- function(birds_per_day) {
+  tail(birds_per_day, 1)
+}
+
+increment_todays_count <- function(birds_per_day) {
+  # clunky!
+  birds_per_day[length(birds_per_day)] <-
+    birds_per_day[length(birds_per_day)] + 1
+  birds_per_day
+}
+
+has_day_without_birds <- function(birds_per_day) {
+  any(birds_per_day == 0)
+}
+
+count_for_first_days <- function(birds_per_day, num_days) {
+  sum(birds_per_day[1:num_days])
+}
+
+busy_days <- function(birds_per_day) {
+  length(birds_per_day[birds_per_day >= 5])
+}

exercises/concept/bird-watcher/bird-watcher.R

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+today <- function(birds_per_day) {
+}
+
+increment_todays_count <- function(birds_per_day) {
+}
+
+has_day_without_birds <- function(birds_per_day) {
+}
+
+count_for_first_days <- function(birds_per_day, num_days) {
+}
+
+busy_days <- function(birds_per_day) {
+}

exercises/concept/bird-watcher/test_bird-watcher.R

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+source("./bird-watcher.R")
+library(testthat)
+
+# 1) today
+
+test_that("Today for disappointing day", {
+  birds_per_day <- c(0, 0, 1, 0, 0, 1, 0)
+  expect_equal(today(birds_per_day), 0)
+})
+
+test_that("Today for busy day", {
+  birds_per_day <- c(8, 8, 9, 5, 4, 7, 10)
+  expect_equal(today(birds_per_day), 10)
+})
+
+# 2) increment_todays_count
+
+test_that("Increment todays count with no previous visits", {
+  birds_per_day <- c(0, 0, 0, 4, 2, 3, 0)
+  expect_equal(
+    increment_todays_count(birds_per_day),
+    c(0, 0, 0, 4, 2, 3, 1)
+  )
+})
+
+test_that("Increment todays count with multiple previous visits", {
+  birds_per_day <- c(8, 8, 9, 2, 1, 6, 4)
+  expect_equal(
+    increment_todays_count(birds_per_day),
+    c(8, 8, 9, 2, 1, 6, 5)
+  )
+})
+
+# 3) has_day_without_birds
+
+test_that("Has day without birds with day without birds", {
+  birds_per_day <- c(5, 5, 4, 0, 7, 6, 7)
+  expect_equal(has_day_without_birds(birds_per_day), TRUE)
+})
+
+test_that("Has day without birds with no day without birds", {
+  birds_per_day <- c(4, 5, 9, 10, 9, 4, 3)
+  expect_equal(has_day_without_birds(birds_per_day), FALSE)
+})
+
+# 4) count_for_first_days
+
+test_that("Count for first three days of disappointing week", {
+  birds_per_day <- c(0, 0, 1, 0, 0, 1, 0)
+  expect_equal(count_for_first_days(birds_per_day, 3), 1)
+})
+
+test_that("Count for first six days of busy week", {
+  birds_per_day <- c(5, 9, 12, 6, 8, 8, 17)
+  expect_equal(count_for_first_days(birds_per_day, 6), 48)
+})
+
+# 5) busy_days
+
+test_that("Busy days for disappointing week", {
+  birds_per_day <- c(1, 1, 1, 0, 0, 0, 0)
+  expect_equal(busy_days(birds_per_day), 0)
+})
+
+test_that("Busy days for busy week", {
+  birds_per_day <- c(4, 9, 5, 7, 8, 8, 2)
+  expect_equal(busy_days(birds_per_day), 5)
+})