Ruby Split String Examples

Split. Strings often contain blocks of data.

With split, we separate these blocks based on a delimiter. In Ruby, a string, or a regular expression, is used as the separator.

Split is powerful. This method is widely used. When we omit an argument, it separates a string on spaces. This is the default behavior.

First example. Please consider the input string here: it contains three words. Each one is separated with a single space character.

Then: We call split(), specifying a space as the delimiter character. This separates those three words.

Array: The resulting array has three string elements. We loop over these with the each iterator.

Based on:

Ruby 2

Ruby program that uses split

# Split this string on a space.
input = "one two three"
values = input.split(" ")

# Display each value to the console.
values.each do |value|
    puts value
end

Output

one
two
three

No arguments. No arguments are required to split on a space character. The space delimiter is implicit: you do not need to specify it. This can make some programs easier to read.

But: Perhaps a comment would help in this case. Usually split() is called with a delimiter, so this may not be as expected.

Ruby program that uses split, no arguments

input = "a b c"
# We do not specify an argument: space is implicit.
values = input.split()
puts values

Output

a
b
c

Regexp. Split does not require a simple string argument. It can act also upon a regular expression (regexp). In Ruby we specify these with forward slashes.

Here: We specify a delimiter of one or more non-word characters. The Kleene closure + indicates "one or more."

Tip: The delimiter here matches one or two characters. It includes both the comma and the following space.

So: The resulting string array has no empty values. It contains just the four words stored within the text.

Ruby program that uses Regexp to split

value = "one, two three: four"

# Split on one or more non-word characters.
a = value.split(/\W+/)

# Display result.
puts a

Output

one
two
three
four

Regexp pattern

\W+     One or more non-word characters.

Limit. This is the maximum number of array elements that are returned. If more elements are found than are allowed by the limit, the excess ones are grouped in the final array element.

Tip: Limiting the number of array elements can be useful if you only need the first several parts from a string.

Ruby program that splits with limit

# Contains five vegetable names.
value = "carrot,squash,corn,broccoli,spinach"

# Split with limit of 3.
vegetables = value.split(",", 3)
puts vegetables

Output

carrot
squash
corn,broccoli,spinach

Empty. Often the split method will return empty entries. These are caused by having two delimiters with no interior content. We can invoke delete_if to remove these empty elements.

So: We use an iterator block. We delete all elements that are zero chars. The empty entry, between "cat" and "dog," is removed.

Ruby program that removes empty entries

# Split on a comma.
value = "cat,,dog,bird"
elements = value.split(",")
print elements, "\n"

# Remove empty elements from the array.
elements.delete_if{|e| e.length == 0}
print elements

Output

["cat", "", "dog", "bird"]
["cat", "dog", "bird"]

Characters. With split we can get the characters from a string. Pass an empty string literal ("") to the split method. The length of the array equals the length of the string.

Ruby program that splits characters

value = "xyz 1"

# Separate chars.
array = value.split ""

# Write length.
puts array.length

# Write elements.
print array

Output

5
["x", "y", "z", " ", "1"]

File. Often we need to handle CSV files. We first use the IO.foreach iterator to easily loop over the lines in a text file. Each line must be chomped to remove the trailing newline.

Then: We use split() on the commas. The parts between the comma chars are returned in an array.

Output: The program writes the contents of the Array returned by split. It also prints the length of that Array.

Example file: csv.txt

cat,tiger,meow,100
airplane,bird,200
tree,grove,400
sand,beach,fish,50

Ruby program that splits lines in file

# Open this file (change file name for your program).
IO.foreach("/files/csv.txt") do |line|

    # Remove trailing whitespace.
    line.chomp!

    # Split on comma.
    values = line.split(",")

    # Write results.
    print values.join("+") << "... " << String(values.length) << "\n"

end

Output

cat+tiger+meow+100... 4
airplane+bird+200... 3
tree+grove+400... 3
sand+beach+fish+50... 4

Join. This is not a string method. Instead it acts on string arrays (or arrays of any type of element that are converted into strings). We can use join to round-trip our data with split().

String Arrays

Ruby that uses join

values = ["keyboard", "monitor", "CPU"]

# Use the join method to combine a string array.
joined = values.join(";")
puts joined

Output

keyboard;monitor;CPU

Parse integers. Often we need to parse integer values that are in a CSV format. We first split the line, and then use Integer to convert each string.

Here: We display each number in the string that is equal to or greater than 200. The value 100 is not displayed.

Ruby that uses split, parses Integers

line = "100,200,300"

# Split on the comma char.
values = line.split(",")

# Parse each number in the result array.
values.each do |v|
    number = Integer(v)

    # Display number if it is greater than or equal to 200.
    if number >= 200
	puts number
    end
end

Output

200
300

In CSV files, input lines contain separating characters. We do not need a special parsing method to extract the inner strings. Split(), with a special delimiter, works well.

Delimiters. We learned how to split based on a string delimiter. A regular expression offers more power. And finally we used join to combine strings in an Array.

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