How to convert a array of strings to an array of symbols?

Question

I want to convert the elements of the string array below to symbols, and output them

strings = ["HTML", "CSS", "JavaScript", "Python", "Ruby"]

look at what I'm doing:

strings.each { |x| puts x.to_sym }

No success. What am I doing wrong?

Possible Duplicate of http://stackoverflow.com/questions/800122/best-way-to-convert-strings-to-symbols-in-hash — , May 12 '13 at 00:00
@Abe: That's for keys of a hash. This is for array elements. — icktoofay, May 12 '13 at 00:04
@Abe That is not a dup, it's for hashes. (edit: icktoofay beat me to it :P) — tckmn, May 12 '13 at 00:04
@icktofay I see, but it would be easy to convert them, right? — , May 12 '13 at 00:05
@Abe That doesn't mean it's a duplicate.... Also, not really. Do you know Ruby? — tckmn, May 12 '13 at 00:05
@Abe: Maybe, but you'd have a cleaner answer if you just started out trying to do it with an array. — icktoofay, May 12 '13 at 00:05
@Doorknob Not really I confess :P But I'll keep the comment because it got an up vote — , May 12 '13 at 00:05
For those saying the link recommended by @Abe isn't applicable, it is. The keys of a hash *ARE* an array. `{'a'=>1}.keys.class => Array`. The problem is you have to know how to identify where that array is being massaged from strings into a symbol. — the Tin Man, May 12 '13 at 01:00
@Abe probably this is more of a duplicate of http://stackoverflow.com/questions/6496931/apply-method-to-array-elements — lulalala, May 17 '13 at 02:53
@lulalala perhaps, but that's more of a global area rather than a local idea. — , May 18 '13 at 00:02

icktoofay · Answer 1 · 2013-05-12T00:08:56.120

Use map rather than each:

>> strings.map { |x| x.to_sym }
=> [:HTML, :CSS, :JavaScript, :Python, :Ruby]

For Ruby 1.8.7 and later or with ActiveSupport included, you can use this syntax:

>> strings.map &:to_sym
=> [:HTML, :CSS, :JavaScript, :Python, :Ruby]

The reason your each method appears to not work is that calling puts with a symbol outputs the string representation of the symbol (that is, without the :). Additionally, you're just looping through and outputting things; you're not actually constructing a new array.

score 33 · Answer 2 · answered Oct 06 '15 at 13:07

33

Clean one-liner:

%w(HTML CSS JavaScript Python Ruby).map(&:to_sym)

& tells argument should be treated as a block, i.e. build up array and apply to_sym to each element.

answered Oct 06 '15 at 13:07

cb24

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Your answer is the cleanest of all, also I Benchmarked it and checked its performance on different kind of arrays. I wasn't sure if it was better to give a new answer based on yours or just edit this one. – Lomefin Jul 09 '16 at 00:37

DaniG2k · Answer 3 · 2015-08-29T10:24:05.193

10

I'd do something like

strings.map! &:to_sym

edited Aug 29 '15 at 10:24

answered Feb 17 '15 at 19:37

DaniG2k

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score 4 · Answer 4 · edited May 23 '17 at 12:02

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icktoofay already gave the correct answer.

On additional remark: With

strings.map { |x| x.to_sym }

you get a new array, the original array is unchanged.

To use it, you can assign it to another variable:

string2 = strings.map { |x| x.to_sym }

If you want to modify string, you can use map!:

strings.map! { |x| x.to_sym }

edited May 23 '17 at 12:02

Community

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answered May 12 '13 at 18:08

knut

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score 2 · Answer 5 · edited Dec 03 '15 at 21:21

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@icktoofay has the correct answer, but just to help you better understand the each method, here is how you can do the same thing using each:

strings = ["HTML", "CSS", "JavaScript", "Python", "Ruby"]
symbols = [] # an empty array to hold our symbols
strings.each { |s| symbols << s.to_sym }

edited Dec 03 '15 at 21:21

Michaël Witrant

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answered May 12 '13 at 00:10

Teddy

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score 1 · Answer 6 · answered Jul 09 '16 at 00:36

@cb24's answer is generally the most appropiate, I wanted to compare that solution with another one

strings.collect {|x| x.to_sym }

I did some benchmarks and @cb24's answer works best in most cases, when there are some more elements in the array, but if it happens to be a very tiny array, the collect method works a little faster.

I publish here the code and the results, this is my real first benchmark so if I got something wrong some feedback would be appreciated. I did it on both String -> Symbol and Symbol -> String

n = 1000000 

a = [:a,:b,:c,:d,:e,:f,:g,:h,:i].freeze #A "long" array of symbols

Benchmark.bm do |x|
  x.report { n.times { a.map(&:to_s)} }
  x.report { n.times { a.collect{|x| x.to_s}} }
end  

       user     system      total        real
   2.040000   0.010000   2.050000 (  2.056784)
   2.100000   0.010000   2.110000 (  2.118546)


b = [:a, :b].freeze  #Small array

Benchmark.bm do |x|
  x.report { n.times { b.map(&:to_s)} }
  x.report { n.times { b.collect{|x| x.to_s}} }
end  


       user     system      total        real
   0.610000   0.000000   0.610000 (  0.622231)
   0.530000   0.010000   0.540000 (  0.536087)



w = %w(a b).freeze  #Again, a small array, now of Strings
Benchmark.bm do |x|
  x.report { n.times { w.map(&:to_sym)} }
  x.report { n.times { w.collect{|x| x.to_sym}} }
end 

       user     system      total        real
   0.510000   0.000000   0.510000 (  0.519337)
   0.440000   0.010000   0.450000 (  0.447990)



y = %w(a b c d e f g h i j k l m n o p q).freeze #And a pretty long one
Benchmark.bm do |x|
  x.report { n.times { y.map(&:to_sym)} }
  x.report { n.times { y.collect{|x| x.to_sym}} }
end 

       user     system      total        real
   2.870000   0.030000   2.900000 (  2.928830)
   3.240000   0.030000   3.270000 (  3.371295)

The inflection points I didn't calculate but it is quite interesting, I read somewhere that some improvements where made with short arrays, since most of them are just a couple of elements long.

Frank Koehl · Answer 7 · 2018-08-09T18:02:06.693

If you want to go the gem route, finishing_moves has an Array#to_sym_strict method that does exactly what you're looking for:

strings = ["HTML", "CSS", "JavaScript", "Python", "Ruby"]
strings.to_sym_strict
# => [:HTML, :CSS, :JavaScript, :Python, :Ruby]

There's also a #to_sym_loose to handle arrays of mixed type:

strings = ["HTML", "CSS", "JavaScript", "Python", "Ruby", 1, /a regex/, {a: :hash}]
strings.to_sym_loose
# => [:HTML, :CSS, :JavaScript, :Python, :Ruby, 1, /a regex/, {a: :hash}]
# no exceptions thrown

score 0 · Answer 8 · edited Apr 11 '15 at 02:39

0

Or can be done as follows:

strings.each do |s|  
symbols.push(s.to_sym)

edited Apr 11 '15 at 02:39

blackbishop

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answered Apr 11 '15 at 02:05

Harsha

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score 0 · Answer 9 · answered Apr 14 '21 at 19:46

0

In the interest of completeness you can also make use of the %i string literal since at least Ruby 2.0.0 to start off with an array of symbols.

%i[HTML CSS JavaScript Python Ruby]
# => [:HTML, :CSS, :JavaScript, :Python, :Ruby]

answered Apr 14 '21 at 19:46

diemer

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How to convert a array of strings to an array of symbols?

9 Answers9