Question

I tried the following and it was partly working:

>> s.methods.map {|n| n if n =~ /time/}
=> [nil, nil, nil, nil, nil, nil, nil, nil, "skip_time_zone_conversion_for_attri
butes", nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, ni
l, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, ni
l, "timestamped_migrations", nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, n
il, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, n
il, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, n
il, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, n
il, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, "time_zone_aware
_attributes", nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, n
il, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, "default_timezone", nil, n
il, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, n
il, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, n
il, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, n
il, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, "recor
d_timestamps", nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil, nil,
nil, nil, nil, nil, nil, nil, nil]

>> s.methods.each {|n| p n if n =~ /time/}
"skip_time_zone_conversion_for_attributes"
"timestamped_migrations"
"time_zone_aware_attributes"
"default_timezone"
"record_timestamps"
=> ["extended_by", "before_create", "vote_ids=", "save_without_dirty", "_delete"
, "touch", "daemonize", "after_destroy", "skip_time_zone_conversion_for_attribut
es", "methods", "send", "to_query", "becomes", "after_validation", "store_full_s
ti_class?", "save_with_transactions!", "autosave_associated_records_for_votes",
"require_library_or_gem", "enum_for", "taint", "instance_variable_defined?", "ac
     [...] and the rest of the whole array

>> s.methods.filter {|n| n =~ /time/}
NoMethodError: undefined method `filter' for #<Array:0x4de6b00>
        from (irb):93

Answer 1

grep is another easy way to accomplish this:

1.9.0 > require 'date'
 => true 
1.9.0 > x = Date.new
 => #<Date: -1/2,0,2299161> 
1.9.0 > x.methods.grep /time/
 => ["ctime", "asctime", "strftime"] 

With the approaches you tried:

map applies the given block to each element of the given enumerable, returning a new enumerable. That’s not what you wanted here (as you saw).

methods.each sort of works, but obviously simply printing out the results isn’t terribly useful. It wouldn’t be Ruby-like at all, but you could have done:

matching_methods = []
s.methods.each {|m| matching_methods << m if m =~ /time/}

to accumulate each method matching /time/ into the matching_methods array. Of course, if you’re doing that, then

s.methods.select { |m| m =~ /time/ }

is preferable.

Lastly, filter doesn’t exist in Ruby; that’s what select (or find_all) is for.