I am trying to create a program where the first three characters of a string is repeated a given number of times like this:
foo('Chocolate', 3) # => 'ChoChoCho'
foo('Abc', 3) # => 'AbcAbcAbc'
I know I can use length to count characters, but how do I specify the length of the string to be outputted? Also how can I specify the number of times?
def foo(str, n)
str[0..2] * n
end
You can use something like this.
def print_first_three_x_times(string, x)
#remove everything but the first three chars
string.slice!(3..string.length)
#print x times
x.times{ print string }
end
output:
Hunter#Hunter-PC ~
$ irb
irb(main):008:0> print_first_three_x_times("Hunter",5)
HunHunHunHunHun=> 5
irb(main):009:0>
Related
I'm very new to Ruby and searching for a solution.
Essentially I have a hash in the form of [0 > String, 1 > String] etc.
I want to run a loop which can count the characters in the strings in the hashes, should it reach a limit, the end of the string should be cut at that point and replaced with '...'
Example:
Say I set my character count at 10:
Hello World!
Would shorten to:
Hello Worl...
May be worth noting that this hash is created from an array, as such if it is deemed wiser to do it before the hash conversion, that would also be fine. Any advice is hugely appreciated.
Using ActiveSupport's Truncate Method
If you're willing to mix in methods from the ActiveSupport gem such as String#truncate, this is trivial. For example:
require 'active_support/core_ext/string/filters'
'Hello World!'.truncate 10
#=> "Hello W..."
Note that the #truncate method counts the ellipsis as three characters (one for each period in the ellipsis) towards the total character count. Bump your count by three characters (e.g. 13 instead of 10) if you actually want 10 characters before the ellipsis rather than including it.
I think this is not beautiful, but it does what you're asking:
hash = {
0 => 'hello world',
1 => 'hello'
}
hash.each_pair do |key, value|
p key: key
p value: value.length > 10 ? value[0..9] + '...' : value
end
you could also make a method to truncate the string, like this:
def truncate(string, truncate_after)
return string if string.length < truncate_after
string[0..(truncate_after - 1)] + '...'
end
This may be a really simple regex but its one of those problems that have proven hard to google.
I have error codes coming back from a third party system. They are supposed to be in the format:
ZZZ##
where Z is Alpha and # is numeric. They are supposed to be 0 padded, but i'm finding that sometimes they come back
ZZZ#
without the 0 padding.
Anyone know how i could add the 0 padding so i can use the string as an index to a hash?
Here's my take:
def pad str
number = str.scan(/\d+/).first
str[number] = "%02d" % number.to_i
str
end
6.times do |n|
puts pad "ZZZ#{7 + n}"
end
# >> ZZZ07
# >> ZZZ08
# >> ZZZ09
# >> ZZZ10
# >> ZZZ11
# >> ZZZ12
Reading:
String#[]=
Kernel#sprintf and formatting flags.
fixed = str.gsub /([a-z]{3})(\d)(?=\D|\z)/i, '\10\2'
That says:
Find three letters
…followed by a digit
…and make sure that then you see either a non-digit or the end of file
and replace with the three letters (\1), a zero (0), and then the digit (\2)
To pad to an arbitrary length, you could:
# Pad to six digits
fixed = str.gsub /([a-z]{3})(\d+)/i do
"%s%06d" % [ $1, $2.to_i ]
end
Here's mine:
"ZZZ7".gsub(/\d+/){|x| "%02d" % x}
=> "ZZZ07"
There's probably a million ways to do this but here's another look.
str.gsub!(/[0-9]+/ , '0\0' ) if str.length < 5
What is the preferred way of removing the last n characters from a string?
irb> 'now is the time'[0...-4]
=> "now is the "
If the characters you want to remove are always the same characters, then consider chomp:
'abc123'.chomp('123') # => "abc"
The advantages of chomp are: no counting, and the code more clearly communicates what it is doing.
With no arguments, chomp removes the DOS or Unix line ending, if either is present:
"abc\n".chomp # => "abc"
"abc\r\n".chomp # => "abc"
From the comments, there was a question of the speed of using #chomp versus using a range. Here is a benchmark comparing the two:
require 'benchmark'
S = 'asdfghjkl'
SL = S.length
T = 10_000
A = 1_000.times.map { |n| "#{n}#{S}" }
GC.disable
Benchmark.bmbm do |x|
x.report('chomp') { T.times { A.each { |s| s.chomp(S) } } }
x.report('range') { T.times { A.each { |s| s[0...-SL] } } }
end
Benchmark Results (using CRuby 2.13p242):
Rehearsal -----------------------------------------
chomp 1.540000 0.040000 1.580000 ( 1.587908)
range 1.810000 0.200000 2.010000 ( 2.011846)
-------------------------------- total: 3.590000sec
user system total real
chomp 1.550000 0.070000 1.620000 ( 1.610362)
range 1.970000 0.170000 2.140000 ( 2.146682)
So chomp is faster than using a range, by ~22%.
Ruby 2.5+
As of Ruby 2.5 you can use delete_suffix or delete_suffix! to achieve this in a fast and readable manner.
The docs on the methods are here.
If you know what the suffix is, this is idiomatic (and I'd argue, even more readable than other answers here):
'abc123'.delete_suffix('123') # => "abc"
'abc123'.delete_suffix!('123') # => "abc"
It's even significantly faster (almost 40% with the bang method) than the top answer. Here's the result of the same benchmark:
user system total real
chomp 0.949823 0.001025 0.950848 ( 0.951941)
range 1.874237 0.001472 1.875709 ( 1.876820)
delete_suffix 0.721699 0.000945 0.722644 ( 0.723410)
delete_suffix! 0.650042 0.000714 0.650756 ( 0.651332)
I hope this is useful - note the method doesn't currently accept a regex so if you don't know the suffix it's not viable for the time being. However, as the accepted answer (update: at the time of writing) dictates the same, I thought this might be useful to some people.
str = str[0..-1-n]
Unlike the [0...-n], this handles the case of n=0.
I would suggest chop. I think it has been mentioned in one of the comments but without links or explanations so here's why I think it's better:
It simply removes the last character from a string and you don't have to specify any values for that to happen.
If you need to remove more than one character then chomp is your best bet. This is what the ruby docs have to say about chop:
Returns a new String with the last character removed. If the string
ends with \r\n, both characters are removed. Applying chop to an empty
string returns an empty string. String#chomp is often a safer
alternative, as it leaves the string unchanged if it doesn’t end in a
record separator.
Although this is used mostly to remove separators such as \r\n I've used it to remove the last character from a simple string, for example the s to make the word singular.
name = "my text"
x.times do name.chop! end
Here in the console:
>name = "Nabucodonosor"
=> "Nabucodonosor"
> 7.times do name.chop! end
=> 7
> name
=> "Nabuco"
Dropping the last n characters is the same as keeping the first length - n characters.
Active Support includes String#first and String#last methods which provide a convenient way to keep or drop the first/last n characters:
require 'active_support/core_ext/string/access'
"foobarbaz".first(3) # => "foo"
"foobarbaz".first(-3) # => "foobar"
"foobarbaz".last(3) # => "baz"
"foobarbaz".last(-3) # => "barbaz"
if you are using rails, try:
"my_string".last(2) # => "ng"
[EDITED]
To get the string WITHOUT the last 2 chars:
n = "my_string".size
"my_string"[0..n-3] # => "my_stri"
Note: the last string char is at n-1. So, to remove the last 2, we use n-3.
Check out the slice() method:
http://ruby-doc.org/core-2.5.0/String.html#method-i-slice
You can always use something like
"string".sub!(/.{X}$/,'')
Where X is the number of characters to remove.
Or with assigning/using the result:
myvar = "string"[0..-X]
where X is the number of characters plus one to remove.
If you're ok with creating class methods and want the characters you chop off, try this:
class String
def chop_multiple(amount)
amount.times.inject([self, '']){ |(s, r)| [s.chop, r.prepend(s[-1])] }
end
end
hello, world = "hello world".chop_multiple 5
hello #=> 'hello '
world #=> 'world'
Using regex:
str = 'string'
n = 2 #to remove last n characters
str[/\A.{#{str.size-n}}/] #=> "stri"
x = "my_test"
last_char = x.split('').last
In Ruby language, how can I get the number of lines in a string?
There is a lines method for strings which returns an Enumerator. Call count on the enumerator.
str = "Hello\nWorld"
str.lines.count # 2
str = "Hello\nWorld\n" # trailing newline is ignored
str.lines.count # 2
The lines method was introduced in Ruby 1.8.7. If you're using an older version, checkout the answers by #mipadi and #Greg.
One way would be to count the number of line endings (\n or \r\n, depending on the string), the caveat being that if the string does not end in a new line, you'll have to make sure to add one to your count. You could do so with the following:
c = my_string.count("\n")
c += 1 unless c[-1,1] == "\n"
You could also just loop through the string and count the lines:
c = 0
my_string.each { |line| c += 1 }
Continuing with that solution, you could get really fancy and use inject:
c = my_string.each.inject(0) { |count, line| count += 1 }
string".split("\n").size works nicely. I like that it ignores trailing new-lines if they don't contain content.
"Hello\nWorld\n".split("\n") # => ["Hello", "World"]
"hello\nworld\nfoo bar\n\n".split("\n").size # => 3
That might not be what you want, so use lines() as #Anurag suggested instead if you need to honor all new-lines.
"hello\nworld\nfoo bar\n\n".lines.count # => 4
"hello\nworld\nfoo bar\n\n".chomp.split("\n",-1).size # => 4
String#chomp gets rid of an end of line if it exists, and the -1 allows empty strings.
given a file object (here, in rails)
file = File.open(File.join(Rails.root, 'lib', 'file.json'))
file.readlines.count
returns the number of lines
IO#readlines performs a split method on strings (IOStrings in this case) using newlines as the separator
This will not count blank lines:
string.split("\n").select{ |line| line != "" }.size
One\n
Two\n
Three\n
Four\n
remove_lines(2) would remove the first two lines, leaving the string:
Three\n
Four\n
s.to_a[2..-1].join
>> s = "One\nTwo\nThree\nFour\n"
=> "One\nTwo\nThree\nFour\n"
>> s.to_a[2..-1].join
=> "Three\nFour\n"
s = "One\nTwo\nThree\nFour"
lines = s.lines
> ["One\n", "Two\n", "Three\n", "Four"]
remaining_lines = lines[2..-1]
> ["Three\n", "Four"]
remaining_lines.join
> "Three\nFour"
String#lines converts the string into an array of lines (retaining the new line character at the end of each string)
[2..-1] specifies the range of lines to return, in this case the third through the last
Array#join concatenates the lines back together, without any space (but since the lines still contain the new line character, we don't need a separator)
In one line:
s.lines[2..-1].join
class String
def remove_lines(i)
split("\n")[i..-1].join("\n")
end
end
Calling "One\nTwo\nThree\nFour\n".remove_lines(2) would result in "Three\nFour". If you need the trailing "\n" you need to extend this method accordingly.
I had a situation where I needed to support multiple platform EOLN (both \r and \n), and had success with the following:
split(/\r\n|\r|\n/, 2).last
Or the equivalent remove_lines:
def remove_lines(number_of_lines=1)
split(/\r\n|\r|\n/, number_of_lines+1).last
end
Here is a pure regexp one-liner. Hypothetically it should be even faster than the elegant solution provided by #DigitalRoss:
n = 4 # number of lines
str.gsub(/\A(.*\n){#{n}}/,'')
If you know in advance how many line you want to cut (4 here):
str.gsub(/\A(.*\n){4}/,'')
And if you want to cut only one line:
str.gsub(/\A.*\n/,'')
In order to cut n lines from the tail:
gsub(/(\n.*){#{n}}\Z/,'')
This problem will remove the first two lines using regular expression.
Text = "One\nTwo\nThree\nFour"
Text = Text.gsub /^(?:[^\n]*\n){2}/, ''
# -----------------------------------^^ (2) Replace with nothing
# ----------------^^^^^^^^^^^^^^^^ (1) Detect first 2 lines
puts Text
EDIT: I've just saw that the question is also about 'n' lines not just two lines.
So here is my new answer.
Lines_Removed = 2
Original_Text = "One\nTwo\nThree\nFour"
Result___Text = (Original_Text.gsub(Regexp.new("([^\n]*\n){%s}" % Lines_Removed), ''))
# ^^^^^^^^^^^^^^ ^^
# - (1) Detect first lines -----++++++++++++++ ||
# - (2) Replace with nothing -----------------------------------------------------++
puts Result___Text # Returns "Three\nFour"
def remove_lines(str, n)
res = ""
arr = str.split("\n")[n..(str.size-n)]
arr.each { |i| res.concat(i + "\n") }
return res
end
a = "1\n2\n3\n4\n"
b = remove_lines(a, 2)
print b