Is there a better way to ignore uppercase than this?
"Hello".start_with?("hell","Hell") #=> true
I want to check if a string element in an array starts with another string ignoring uppercase, like LIKE % in MySQL.
I would do something like this:
'Hello'.upcase.start_with?('HELL')
Another approach to the same problem. That's equivalent to do something like UPPER(column) like 'SOMETHING%' in SQL.
You could use a regular expression with String#=~:
"Hello" =~ /^hell/i #=> 0
"hELLO" =~ /^hell/i #=> 0
"world" =~ /^hell/i #=> nil
Since 0 is truthy and nil is falsy this can be used in an if clause:
if str =~ /^hell/i
# starts with hell
end
I think the best is to use Ruby's regex matching with ignore case flag:
'Hello'.match /^hell/i
The '^' designates the start of the string. Without it would match 'hell' anywhere in the string. And the last 'i' is just a regex flag to indicate matching with ignore case set.
You can find more info on Ruby Regex API here:
http://www.regular-expressions.info/ruby.html
Related
I am new to ruby, I am trying to write a method that checks if the word includes "hello" case insensitive e.g "HelLO" would still be true.
I can think of two approaches:
downcase before comparing
str = "HelLO"
str.downcase.include?('hello')
#=> true
use case-insensitive regular rexpression
str = "HelLO"
str.match?(/hello/i)
#=> true
I think the easiest approach is to downcase both string and do the comparing. Like this:
'HellO'.downcase.include?('hello')
# true
So I've got an issue where my regex looks like this: /true|false/.
When I check the word falsee I get a true from this regex, is there a way to just limit it to the exact true or false words?
Use this regex:
/^(true|false)$/
It will match the beginning and end of the test string with ^ and $, respectively, so nothing else can be in the string (exact match).
See live example at Regex101.
UPDATE (see #w0lf's comment): The parentheses are to isolate the true|false clause so that they are not grouped incorrectly. (This also puts the true or false match in the first capturing group, but since it seems that you are only matching and not capturing an output, this should not make a difference).
Alternatively, if you simply want to match two values, there are easier ways in Ruby. #SimoneCarletti suggests one. You can also use the basic == or eql? operators. Try running the following script to see that these all work:
values = ["true", "false", "almosttrue", "falsealmost"]
values.each do | value |
puts value
# these three are all equivalent
puts "match with if" if value == "true" || value == "false"
puts "match with equals?" if (value.eql? "true") || (value.eql? "false")
puts "match with regex" if /^(true|false)$/.match value
puts
end
You need to use the ^ and $ anchors:
/^(true|false)$/
Edit: As Cary pointed out in the comments, the pattern above will also match multiline strings that happen to contain a line with true or false. To avoid this, use the \A and \z delimiters that match the beginning and end of string respectively:
/\A(true|false)\z/
Try out
/^(true|false)$/
where ^ is the start of a line and $ the end.
You can use
/^(true|false)$/
or even better
/\A(true|false)\z/
that will match the beginning and end of the string (instead of line). If you only need to match for whose words, it may be more efficient to use a simple array and include?:
%w( true false ).include?(value)
I saw this on a screencast and couldn't figure out what it was. Reference sheets just pile it in with other operators as a general pattern match operator.
It matches string to a regular expression.
'hello' =~ /^h/ # => 0
If there is no match, it will return nil. If you pass it invalid arguments (ie, left or right-hand sides are not correct), it will either throw a TypeError or return false.
From ruby-doc :
str =~ obj => fixnum or nil
Match—If obj is a Regexp, use it as a pattern to match against str, and returns the offset position the match starts, or nil if there is no match. Otherwise, invokes obj.=~, passing str as an argument. The default =~ in Object returns false.
"cat o' 9 tails" =~ /\d/ #=> 7
"cat o' 9 tails" =~ 9 #=> false
Well, the reference is correct, it is the "matches this regex" operator.
if var =~ /myregex/ then something end
As the other answers already stated, =~ is the regular expression vs string match operator.
Note: The =~ operator is not commutative
Please consider the note below from the ruby doc site, as I have seen yet only the first form
str =~ regexp
used in the other answers:
Note: str =~ regexp is not the same as regexp =~ str. Strings captured
from named capture groups are assigned to local variables only in the
second case.
Here is the documentation for the second form: link
Regular expression string matching. Here's a detailed list of operators: http://phrogz.net/programmingruby/tut_expressions.html#table_7.1
Regular expression string matching:
puts true if url =~ /google.com/
You can read '=~' as 'is matching'.
I believe this is a pattern matching operator used with regex.
I'm sure I can do this with a regex, but I can't find any explanation for this behavior using just normal delete!:
#1.9.2
>> "helllom<em>".delete!"<em>"
=> "hlllo"
The docs don't have anything to say about this. Seems to me that it's treating '<em>' as a set. Where is this documented?
Edit: in my defense I was looking for special treatment of < and > in the docs under delete. Didn't see anything about it and tried google, which also didn't have anything to say about that -- because it doesn't exist.
String#delete is one of those unfortunate methods that is difficult to explain (I have no idea what the use case is). In practice, I've always used gsub with an empty string as the second argument.
'helllom<em>'.gsub '<em>', '' # => "helllom"
Note that String#gsub! also has weirdness such that you should not depend on its return value, it will return nil if it does not alter the string, so it is best to use gsub if you depend on the return value, or if you want to mutate the string, then use gsub! but and don't use anything else on that line.
You cannot use String#delete to remove substrings.
Check the API. It removes all the characters from given parameters from the given string.
I your case it removes all occurrences of e, m, < and >.
Straight from the docs:
delete([other_str]+) → new_str
Returns a copy of str with all characters in the intersection of its
arguments deleted. Uses the same rules for building the set of
characters as String#count.
ex:
"hello".delete "l","lo" #=> "heo"
"hello".delete "lo" #=> "he"
"hello".delete "aeiou", "^e" #=> "hell"
"hello".delete "ej-m" #=> "ho"
So every character in the intersection of the two strings is removed.
I saw this on a screencast and couldn't figure out what it was. Reference sheets just pile it in with other operators as a general pattern match operator.
It matches string to a regular expression.
'hello' =~ /^h/ # => 0
If there is no match, it will return nil. If you pass it invalid arguments (ie, left or right-hand sides are not correct), it will either throw a TypeError or return false.
From ruby-doc :
str =~ obj => fixnum or nil
Match—If obj is a Regexp, use it as a pattern to match against str, and returns the offset position the match starts, or nil if there is no match. Otherwise, invokes obj.=~, passing str as an argument. The default =~ in Object returns false.
"cat o' 9 tails" =~ /\d/ #=> 7
"cat o' 9 tails" =~ 9 #=> false
Well, the reference is correct, it is the "matches this regex" operator.
if var =~ /myregex/ then something end
As the other answers already stated, =~ is the regular expression vs string match operator.
Note: The =~ operator is not commutative
Please consider the note below from the ruby doc site, as I have seen yet only the first form
str =~ regexp
used in the other answers:
Note: str =~ regexp is not the same as regexp =~ str. Strings captured
from named capture groups are assigned to local variables only in the
second case.
Here is the documentation for the second form: link
Regular expression string matching. Here's a detailed list of operators: http://phrogz.net/programmingruby/tut_expressions.html#table_7.1
Regular expression string matching:
puts true if url =~ /google.com/
You can read '=~' as 'is matching'.
I believe this is a pattern matching operator used with regex.