---
title: "Programming Foundations — In-Class Code"
author: "Data Skills for Psychology"
date: today
format:
  html:
    toc: true
    toc-depth: 2
    theme: cosmo
    code-overflow: wrap
    df-print: kable
---

## Variables

### Numeric Data

```{r}
n_items <- 20
n_items
```

```{r}
item_time <- 15
survey_time <- n_items * item_time
survey_time
```

Updating a variable using its current value:

```{r}
consent_time <- 100
survey_time <- survey_time + consent_time
survey_time
```

### Character Data

```{r}
survey_type <- "multiple choice"
survey_type
```

Counting characters in a string:

```{r}
nchar(survey_type)
```

### Logical Data

```{r}
2 + 2 == 4
2 + 2 == 5
```

Comparison operators:

```{r}
2 + 2 != 5
3 < 5
5 <= 5
```

Logical operators — NOT, OR, AND:

```{r}
age <- 12
adult <- age >= 18
adult
```

```{r}
!adult
```

```{r}
minor <- TRUE
disability <- FALSE
minor | disability
```

```{r}
consent <- TRUE
complete <- FALSE
consent & complete
```

### Activity: Logical Practice

```{r}
attention_check_1 <- "passed"
attention_check_2 <- "failed"

# create variable use_data
```

### Special Values

```{r}
1 / 0     # Inf
0 / 0     # NaN
NA        # missing data
NULL      # no value
```

## Vectors

### Creating Vectors

```{r}
scale_name <- c("depression", "anxiety", "stress")
scale_name
```

```{r}
raw_score <- c(12, 3, 8)
raw_score
```

```{r}
length(scale_name)
class(raw_score)
```

### Extracting Elements

```{r}
scale_name[1]
scale_name[2]
```

Multiple elements:

```{r}
scale_name[c(1, 2)]
scale_name[1:2]
```

Removing elements:

```{r}
scale_name[-3]
```

### Editing Vectors

```{r}
scale_name <- c("depression", "anxpiety", "stress")
scale_name[2]
```

```{r}
scale_name[2] <- "anxiety"
scale_name
```

### Vector Operations

```{r}
raw_score / 42
```

Element-by-element operations with two vectors:

```{r}
correction <- c(1.05, 1.02, 0.99)
raw_score * correction
```

### Logical Indexing

```{r}
keep <- c(TRUE, TRUE, FALSE)
raw_score[keep]
```

Generating a logical vector with a comparison:

```{r}
ages <- c(19, 34, 7, 67)
adults <- ages >= 18
ages[adults]
```

### Activity: Vector Practice

```{r}
age <- c(19, 34, 7, 67)
age[2]
age[c(2, 3)]
```

```{r}
gender <- c("female", "male", "non-binary", "female")
adult <- age >= 18
gender[adult]
```

## Loops

### The `while` Loop

```{r}
x <- 0
while (x < 1000) {
  x <- x + 179
}
x
```

Tracing the loop with print:

```{r}
x <- 0
while (x < 1000) {
  x <- x + 179
  print(x)
}
```

### The `for` Loop

```{r}
for (value in 1:5) {
  answer <- 137 * value
  print(answer)
}
```

### Looping Over Character Vectors

```{r}
words <- c("it", "was", "the", "dirty", "end", "of", "winter")

for (this_word in words) {
  n_letters <- nchar(this_word)
  block_word <- toupper(this_word)
  cat(block_word, "has", n_letters, "letters\n")
}
```

### Activity: Loop Practice

Times table:

```{r}
for (i in 1:10) {
  print(7 * i)
}
```

Telegram — loop until STOP:

```{r}
telegram <- c("All", "is", "well", "here",
              "STOP", "This", "is", "fine")

word <- ""
ind <- 0
while (word != "STOP") {
  ind <- ind + 1
  word <- telegram[ind]
  print(word)
}
```

## Branches

### `if` and `else`

```{r}
today <- "Monday"

if (today == "Monday") {
  print("I don't like Mondays")
} else {
  print("I'm a happy little automaton")
}
```

### Chaining with `else if`

```{r}
today <- "Wednesday"

if (today == "Monday") {
  print("I don't like Mondays")
} else if (today == "Wednesday") {
  print("Wednesday is beige")
} else {
  print("eh, I have no feelings")
}
```

### Combining Loops and Branches

```{r}
days <- c("Monday", "Tuesday", "Wednesday",
          "Thursday", "Friday")

for (today in days) {
  if (today == "Friday") {
    cat(today, ": TGIF!\n")
  } else {
    cat(today, ": keep going...\n")
  }
}
```

### Activity: Grade Calculator

```{r}
score <- 85

if (score >= 90) {
  print("A")
} else if (score >= 80) {
  print("B")
} else if (score >= 70) {
  print("C")
} else if (score >= 60) {
  print("D")
} else {
  print("F")
}
```

Grading a whole vector:

```{r}
scores <- c(95, 72, 58, 83, 67)

for (s in scores) {
  if (s >= 90) {
    g <- "A"
  } else if (s >= 80) {
    g <- "B"
  } else if (s >= 70) {
    g <- "C"
  } else if (s >= 60) {
    g <- "D"
  } else {
    g <- "F"
  }
  cat("Score:", s, "→ Grade:", g, "\n")
}
```

## Functions

### A Simple Function

```{r}
quadruple <- function(x) {
  y <- x * 4
  return(y)
}

quadruple(10)
quadruple(25)
```

### Default Arguments

```{r}
pow <- function(x, y = 1) {
  out <- x ^ y
  return(out)
}

pow(x = 4, y = 2)
pow(x = 3)
```

### Activity: `round_sqrt`

```{r}
round_sqrt <- function(x, digits = 0) {
  result <- sqrt(x)
  result <- round(result, digits = digits)
  return(result)
}

round_sqrt(17)
round_sqrt(17, digits = 2)
```

### Putting It All Together

A grading function:

```{r}
grade <- function(score) {
  if (score >= 90) return("A")
  if (score >= 80) return("B")
  if (score >= 70) return("C")
  if (score >= 60) return("D")
  return("F")
}

scores <- c(95, 72, 58, 83, 67)
for (s in scores) {
  cat("Score:", s, "→ Grade:", grade(s), "\n")
}
```

### Activity: FizzBuzz

```{r}
fizzbuzz <- function(n) {
  if (n %% 3 == 0 & n %% 5 == 0) {
    cat("FizzBuzz\n")
  } else if (n %% 3 == 0) {
    cat("Fizz\n")
  } else if (n %% 5 == 0) {
    cat("Buzz\n")
  } else {
    cat(n, "\n")
  }
}

for (i in 1:20) {
  fizzbuzz(i)
}
```