# How to Convert an Integer to an Array of Digits in Ruby?

In Ruby, you can convert an integer to an array of digits in the following ways:

## Converting Numeric String to Array of Characters

If you are certain that the integer is always going to be positive, then you can simply do the following:

1. Convert integer to numeric string;
2. Convert numeric string to an array of characters (using `String#chars`);
3. Use `Array#map` to convert each array item to an integer.

For example, this can be implemented like so:

```def num_to_array(num)
# 1: convert integer to string
# 2: convert numeric string to array of chars
# 3: convert each numeric string character to integer
num.to_s.chars.map(&:to_i)
end

print num_to_array(12345) #=> [1, 2, 3, 4, 5]
print num_to_array(0) #=> [0]
```

However, if the integer can also be negative, then the following are some ways in which you can handle the negative sign (`-`) when converting an integer to an array of digits:

### Make the Most Significant Digit Negative:

Making the most significant digit negative means that in the resulting array, if the original number is negative, the first digit will have the negative sign. This means that:

```# 12345 becomes [1, 2, 3, 4, 5]
# -12345 becomes [-1, 2, 3, 4, 5]
```

For example, this can be implemented like so:

```def num_to_array(num)
# 1: convert integer in absolute form to string
# 2: convert string to array of numeric string chars
# 3: convert numeric string chars to integers
digits = num.abs.to_s.chars.map(&:to_i)
# 4: make first digit negative if original number is negative
digits[0] = num < 0 ? -digits[0] : digits[0]

digits
end

print num_to_array(12345) #=> [1, 2, 3, 4, 5]
print num_to_array(-12345) #=> [-1, 2, 3, 4, 5]

print num_to_array(0) #=> [0]
print num_to_array(-0) #=> [0]
```

### Add the Minus Sign as a String:

Adding the minus sign (`-`) as a string means that in the resulting array, if the original number is negative, the first element of the array will have the minus sign as a string:

```# 12345 becomes [1, 2, 3, 4, 5]
# -12345 becomes ['-', 1, 2, 3, 4, 5]
```

For example, this can be implemented like so:

```def num_to_array(num)
# 1: convert integer to string
# 2: convert numeric string to array of chars
digits = num.to_s.chars
# 3: convert each numeric string character to integer
digits.map { | curr_num |
# 4: add '-' as is, if present
(curr_num == "-") ? "-" : curr_num.to_i
}
end

print num_to_array(12345) #=> [1, 2, 3, 4, 5]
print num_to_array(-12345) #=> ["-", 1, 2, 3, 4, 5]

print num_to_array(0) #=> [0]
print num_to_array(-0) #=> [0]
```

Adding a leading digit to represent the sign means that in the resulting array, the first element can be used to represent the sign (i.e. `0` for positive integers and `1` for negative integers):

```# 12345 becomes [0, 1, 2, 3, 4, 5]
# -12345 becomes [1, 1, 2, 3, 4, 5]
```

For example, this can be implemented like so:

```def num_to_array(num)
# 1: convert integer in absolute form to string
# 2: convert numeric string to array of chars
# 3: convert each numeric string character to integer
digits = num.abs.to_s.chars.map(&:to_i)

# 4: add 0 or 1 as first element in array
digits.unshift(num < 0 ? 1 : 0)

digits
end

print num_to_array(12345) #=> [0, 1, 2, 3, 4, 5]
print num_to_array(-12345) #=> [1, 1, 2, 3, 4, 5]

print num_to_array(0) #=> [0, 0]
print num_to_array(-0) #=> [0, 0]
```

## Reducing to Single Digit

If you are certain that the integer is always going to be positive, then you can simply do the following:

1. Create a loop;
2. Add the last digit (i.e. remainder of `x % 10`) as the first element to a new array;
3. Remove the last digit from the integer in each iteration till there are no digits left.

For example, this can be implemented like so:

```def num_to_array(num)
digits = []

# 1: create a loop
loop do
# 2: add last digit as first element in new array
digits.unshift(num % 10)
# 3: remove last digit from integer
num /= 10

# ...till there are no digits left
if num == 0
break
end
end

digits
end

print num_to_array(12345) #=> [1, 2, 3, 4, 5]
print num_to_array(0) #=> [0]
```

However, if the integer can also be negative, then you can handle the negative sign (`-`) in the following ways:

### Make the Most Significant Digit Negative:

Making the most significant digit negative means that in the resulting array, if the original number is negative, the first digit will have the negative sign. This means that:

```# 12345 becomes [1, 2, 3, 4, 5]
# -12345 becomes [-1, 2, 3, 4, 5]
```

For example, this can be implemented like so:

```def num_to_array(num)
# 1: convert integer to absolute form
abs_num = num.abs
digits = []

# 2: create a loop
loop do
# 3: add last digit as first element in new array
digits.unshift(abs_num % 10)
# 4: remove last digit from integer
abs_num /= 10

# ...till there are no digits left
if abs_num == 0
break
end
end

# 5: make first digit negative if original number is negative
if num < 0
digits[0] = -digits[0]
end

digits
end

print num_to_array(12345) #=> [1, 2, 3, 4, 5]
print num_to_array(-12345) #=> [-1, 2, 3, 4, 5]

print num_to_array(0) #=> [0, 0]
print num_to_array(-0) #=> [0, 0]
```

### Add the Minus Sign as a String:

Adding the minus sign (`-`) as a string means that in the resulting array, if the original number is negative, the first element of the array will have the minus sign as a string:

```# 12345 becomes [1, 2, 3, 4, 5]
# -12345 becomes ['-', 1, 2, 3, 4, 5]
```

For example, this can be implemented like so:

```def num_to_array(num)
# 1: convert integer to absolute form
abs_num = num.abs
digits = []

# 2: create a loop
loop do
# 3: add last digit as first element in new array
digits.unshift(abs_num % 10)
# 4: remove last digit from integer
abs_num /= 10

# ...till there are no digits left
if abs_num == 0
break
end
end

# 5: add '-' to front of array
if num < 0
digits.unshift("-")
end

digits
end

print num_to_array(12345) #=> [1, 2, 3, 4, 5]
print num_to_array(-12345) #=> ["-", 1, 2, 3, 4, 5]

print num_to_array(0) #=> [0, 0]
print num_to_array(-0) #=> [0, 0]
```

Adding a leading digit to represent the sign means that in the resulting array, the first element can be used to represent the sign (i.e. `0` for positive integers and `1` for negative integers):

```# 12345 becomes [0, 1, 2, 3, 4, 5]
# -12345 becomes [1, 1, 2, 3, 4, 5]
```

For example, this can be implemented like so:

```def num_to_array(num)
# 1: convert integer to absolute form
abs_num = num.abs
digits = []

# 2: create a loop
loop do
# 3: add last digit as first element in new array
digits.unshift(abs_num % 10)
# 4: remove last digit from integer
abs_num /= 10

# ...till there are no digits left
if abs_num == 0
break
end
end

# 5: add 0 or 1 as first element in array
leading_digit = (num < 0) ? 1 : 0

digits
end

print num_to_array(12345) #=> [0, 1, 2, 3, 4, 5]
print num_to_array(-12345) #=> [1, 1, 2, 3, 4, 5]

print num_to_array(0) #=> [0, 0]
print num_to_array(-0) #=> [0, 0]
```

## Using Regular Expression

If you are certain that the integer is always going to be positive, then you can simply do the following:

1. Use `String#match` with a regular expression to convert numeric string to an array of numeric string characters;
2. Use `Array#map` to convert each array item to an integer.

For example, this can be implemented like so:

```def num_to_array(num)
# 1: use regex to match numbers
# 2: convert each item to an integer
num.to_s.to_enum(:scan, /\d/).map(&:to_i)
end

print num_to_array(12345) #=> [1, 2, 3, 4, 5]
print num_to_array(0) #=> [0]
```

However, if the integer can also be negative, then you can handle the negative sign (`-`) in the following ways:

### Make the Most Significant Digit Negative:

Making the most significant digit negative means that in the resulting array, if the original number is negative, the first digit will have the negative sign:

```# 12345 becomes [1, 2, 3, 4, 5]
# -12345 becomes [-1, 2, 3, 4, 5]
```

For example, this can be implemented like so:

```def num_to_array(num)
# 1: use regex to match '-' (optionally) and numbers
# 2: convert each item to an integer
num.to_s.to_enum(:scan, /-?\d/).map(&:to_i)
end

print num_to_array(12345) #=> [1, 2, 3, 4, 5]
print num_to_array(-12345) #=> [-1, 2, 3, 4, 5]

print num_to_array(0) #=> [0]
print num_to_array(-0) #=> [0]
```

### Add the Minus Sign as a String:

Adding the minus sign (`-`) as a string means that in the resulting array, if the original number is negative, the first element of the array will have the minus sign as a string:

```# 12345 becomes [1, 2, 3, 4, 5]
# -12345 becomes ['-', 1, 2, 3, 4, 5]
```

For example, this can be implemented like so:

```def num_to_array(num)
# 1: use regex to match numbers
# 2: convert each item to an integer
matches = num.to_s.to_enum(:scan, /\d/).map(&:to_i)

# 3: add '-' to the front of array
if num < 0
matches.unshift("-")
end

matches
end

print num_to_array(12345) #=> [1, 2, 3, 4, 5]
print num_to_array(-12345) #=> ["-", 1, 2, 3, 4, 5]

print num_to_array(0) #=> [0, 0]
print num_to_array(-0) #=> [0, 0]
```

Adding a leading digit to represent the sign means that in the resulting array, the first element can be used to represent the sign (i.e. `0` for positive integers and `1` for negative integers):

```# 12345 becomes [0, 1, 2, 3, 4, 5]
# -12345 becomes [1, 1, 2, 3, 4, 5]
```

For example, this can be implemented like so:

```def num_to_array(num)
# 1: use regex to match numbers
# 2: convert each item to an integer
matches = num.to_s.to_enum(:scan, /\d/).map(&:to_i)
# 3: add 0 or 1 as first element in array
matches.unshift(num < 0 ? 1 : 0)

matches
end

print num_to_array(12345) #=> [0, 1, 2, 3, 4, 5]
print num_to_array(-12345) #=> [1, 1, 2, 3, 4, 5]

print num_to_array(0) #=> [0, 0]
print num_to_array(-0) #=> [0, 0]
```

This post was published by Daniyal Hamid. Daniyal currently works as the Head of Engineering in Germany and has 20+ years of experience in software engineering, design and marketing. Please show your love and support by sharing this post.