Array map with regular expression

Question

I have an array as below:

arr = [
  nil,
  6,
  "17 to 23 ||'.'||24 to 25 (add a decimal at 10th place)",
  nil,
  nil,
  "37 to 51 ||'.'||52 to 53 (add a decimal at 100th place)",
  nil
]

I want to convert this array into the following:

arr = [
  nil,
  6,
  "10th",
  nil,
  nil,
  "100th",
  nil
]

i.e from the string "17 to 23 ||'.'||24 to 25 (add a decimal at 10th place)", I need the digits mentioned in the bracket.

I tried the following code, but its not working:

arr.map! {|e| e[/^.*?add.*?(\d+)th.*?$/]}

Do you only have to match ...th? What about ...2nd and ...3rd? — Stefan
– Stefan, Commented Jan 5, 2017 at 10:34

Stefan · Accepted Answer · 2017-01-05 10:53:42Z

6

Your code fails because obj[pattern] only works for strings and not for nil or integers (there is Integer#[] but it does something else):

nil[/foo/] #=> NoMethodError: undefined method `[]' for nil:NilClass
123[/foo/] #=> TypeError: no implicit conversion of Regexp into Integer

You could use =~ instead which is defined on Object and overridden by subclasses, e.g. String:

arr.map {|e| e =~ /(\d+th)/ ? $1 : e }
#=> [nil, 6, "10th", nil, nil, "100th", nil]

If e matches /(\d+th)/, return $1 (the first capture group), otherwise e itself.

You can also use a more specific pattern:

/add a decimal at (\d+th) place/

edited Jan 5, 2017 at 10:53

answered Jan 5, 2017 at 10:40

Stefan

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