CODEWITHSUNDEEP
rubyregexstring
the Tin Man
the Tin Man

Reputation: 160551

What is the fastest way to compare the start or end of a String with a sub-string using Ruby?

Slicing a String "Hello world!"[0, 5] == 'Hello' is a common idiom in Ruby to compare the first or last n characters of a string to another string. Regular expressions can do it too. And then there's start_with? and end_with? which can also do this.

Which should I use for the most speed?

Upvotes: 3

Views: 199

Answers (1)

the Tin Man
the Tin Man

Reputation: 160551

Consider these tests:

require 'fruity'

STR = '!' + ('a'..'z').to_a.join # => "!abcdefghijklmnopqrstuvwxyz"

Results for a single character starting a string:

compare do
  _slice { STR[0] == '!' }
  _start_with { STR.start_with?('!') }
  _regex { !!STR[/^!/] }
end

# >> Running each test 32768 times. Test will take about 1 second.
# >> _start_with is faster than _slice by 2x ± 1.0
# >> _slice is similar to _regex

Results for multiple characters starting a string:

compare do
  _slice { STR[0..4] == '!abcd' }
  _start_with { STR.start_with?('!abcd') }
  _regex { !!STR[/^!abcd/] }
end

# >> Running each test 32768 times. Test will take about 2 seconds.
# >> _start_with is faster than _slice by 2x ± 1.0
# >> _slice is similar to _regex

Results for a single character ending a string:

compare do
  _slice { STR[-1] == 'z' }
  _end_with { STR.end_with?('z') }
  _regex { !!STR[/z$/] }
end

# >> Running each test 32768 times. Test will take about 2 seconds.
# >> _end_with is faster than _slice by 2x ± 1.0
# >> _slice is faster than _regex by 2x ± 1.0

Results for multiple characters ending a string:

compare do
  _slice { STR[-5..-1] == 'vwxyz' }
  _end_with { STR.end_with?('vwxyz') }
  _regex { !!STR[/vwxyz$/] }
end

# >> Running each test 16384 times. Test will take about 1 second.
# >> _end_with is faster than _slice by 2x ± 1.0
# >> _slice is similar to _regex

So, for clarity and speed start_with? and end_with? should be our first choices. If we need to use a pattern then slicing or using a regex are the obvious choices.

Upvotes: 4

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