7

i want to know if it's possible to push in array with auto-creation of array if doesn't exist already, like in PHP:

$toto[] = 'titi';

if $toto is not already defined, it will create array and push 'titi' into. If already exist, it will just push.

in Ruby i have to do:

toto ||= []
toto.push('titi')

It's possible to do this in one line?

Because if i have an loop, it will test "||=" for nothing except the first time:

Person.all.each do |person|    
   toto ||= [] #with 1 billion of person, this line is useless 999 999 999 times...
   toto.push(person.name)

have you a better solution?

thx.

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8
  • 3
    Why don't you put that line outside the loop? Commented Dec 13, 2013 at 15:53
  • @rohit89 you can put it as an answer Commented Dec 13, 2013 at 16:06
  • 1
    if i do that, and they are 0 Person, the array will exist [] instead of to be nil Commented Dec 13, 2013 at 16:10
  • 1
    @Matrix does that really hurt so much? toto = [] unless Person.empty? Commented Dec 13, 2013 at 16:11
  • if i test: "if toto", the result not the same. false positive if toto = [] Commented Dec 13, 2013 at 16:13

5 Answers 5

Reset to default
5 
toto = Person.all.reduce([]) do |arr, person|
  arr << person.name
end

or you could simply pluck the names if they come from the DB

toto = Person.pluck(:name) # SELECT `people.name` FROM `people`
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5 Comments

Note: this only works because Array#<< returns self
What's the difference between pluck and map except the latter requires an extra pretzel?
@JanDvorak map Person.all will initialize entire DB rows as AR objects where Person.pluck(:name) does something like SELECT people.name FROM people
so, the difference is pluck acts before the database query takes place, and builds the query?
@JanDvorak yes - similar to Person.count
4

In a single line it will be as:

toto = (toto || [] ) << 'titi'

and for Person name:

toto = (toto || [] ) << person.name

If you don't need to rewrite the Array do as follows:

( toto ||= [] ) << 'titi'
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1 Comment

if you do that, you overwrite the array. sry i don't see your edit, but you write it in one line, but the test is alwais here...
3

In this case I'd just go straight to each_with_object:

toto = Person.all.each_with_object([]) do |person, toto|
  toto.push(person.name)
end

Alternatively, you could just map it:

toto = Person.all.map(&:name)
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Comments

2

I will do as below :

toto = toto.to_a + Person.all.map(&:name)
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3 Comments

Why the extra toto.to_a and concatenation?
@muistooshort in case toto was non-empty before the loop
@muistooshort Jan Dvorak is right.. But to consider this, if toto not exist, then to avoid error no method, I applied nil#to_a which will give [].
0

if $toto is not already defined, it will create array and push 'titi' into. If already exist, it will just push.

in Ruby i have to do:

toto ||= [] toto.push('titi') It's possible to do this in one line?

Yes answer is:

toto ||= Array.new(1, 'titi')

Because if i have an loop, it will test "||=" for nothing except the first time:

Person.all.each do |person|    
  toto ||= [] #with 1 billion of person, this line is useless 999 999 999 times...
  toto.push(person.name)
end

have you a better solution?

you can use it simple with:

toto ||= Person.all.collect(&:name)
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