# Chapter 2 R Programming Done Wrong

The motivation behind this chapter is to provide a reference guide to the more common mistakes when writing R code.

## 2.1 Beginners Luck

### 2.1.1 Checking for Equality vs. Assignment

The most common error by far that affects programmers is making an assignment when trying to check for equality (and vice versa)

# Assigning in if
if(x = 42) { cat("Life!") }
## Error: unexpected '=' in "if(x ="

# Correct
if(x == 42) { cat("Life!") } 
# Equality Check instead of Assignment
x == 42
## No Error, but prints TRUE or FALSE

# Correct
x = 42

### 2.1.2 Missing object

x
Error: object 'x' not found

# Correct
x = 1
x

### 2.1.3if vectorization usage

As emphasis on vectorization grows, there is a tendency to compare two vectors using the default if() instead of ifelse()

x = 1:5
y = 2:6
if(x > y) { TRUE } else { FALSE }
## Warning messages:
## In if (x > y) { : the condition has length > 1 and only the first element will be used

# Correct, if element-wise comparison required
ifelse(x > y, TRUE, FALSE)

# Correct, if totality-comparison requested
if(all(x > y)) { TRUE } else { FALSE }

### 2.1.4 Vector Recycling

Sometimes the length of vectors are not equal or the data does not divide evenly or oddly when perform a vectorized computation.

x = 1:5
y = 2:3

x + y
## Warning message:
## In x + y : longer object length is not a multiple
## of shorter object length

# Correct
x = 1:4
y = 2:3
x + y
# Repeats y twice
# 1 + 2, 2 + 3, 3 + 2, 4 + 3

## 2.2 Omitting Symbols

### 2.2.1 Mismatched curly brackets {}, parentheses (), or brackets []

Often it is ideal to use parentheses or curly brackets for order of operations, though this sometimes causes a mismatch. A mismatch may also be present with the brackets subset operator []

2*(x + y))
## Error: unexpected ')' in "2*(x + y))"

2*{x + y}}
## Error: unexpected '}' in "2*{x + y}}"

x]1
## Error: unexpected ']' in "x]"

# Corrected
2*((x + y))

2*{{x + y}}

x[1]

### 2.2.2 No Multiplication Symbol

When working on computations, sometimes we just “slip” and opt not to write a multiplication sign thinking the interpreter can understand the context.

2x+4
## Error: unexpected symbol in "2x"

# Correct
2*x + 4

### 2.2.3 Manual Data Entry

Sometimes it’s easier as we’ll see next week to manually enter data. The issue with this is sometimes you forget simple things like a ,.

c(1, 2 3, 4)
## Error: unexpected numeric constant in "c(1,2 3"

# Correct
c(1, 2, 3, 4)

### 2.2.4 Strings in character values

At times, there may come a need to place a quotation inside of a string. To do this, requires using an escape character \ or using '' instead.

"toad"princess"
## Error: unexpected symbol in ""toad"princess"

# Corrected
"toad\"princess"
'toad"princess'

## 2.3 Special Values

### 2.3.1 Handling Missing Value Operations

The NA character indicates the presence of a missing value. These missing values can play havoc with computations.

x = c(1,NA,2)
3 + x
# No Error, but: [1]  4 NA  5

sum(x)
# No Error, but: [1] NA

# Corrected
1 + na.omit(x)    # Deletes NA
sum(x, na.rm = T) # Removes NA inside function

### 2.3.2 Finiteness of Values

R can have some funky finiteness problems due to how NA values are created.

x = c(NA,-Inf, Inf ,NaN)
is.na(x)
# No error, but: [1] TRUE FALSE FALSE TRUE

is.infinite(x)
# No error, but: [1] FALSE TRUE TRUE FALSE

# Correct
is.finite(x)
# [1] FALSE FALSE FALSE FALSE