change date format in array elements

Question

I have certain array elements (strings) that should be formatted as dates (mm/dd/yyyy), and they are currently causing issues when the day portion of the date is a single digit. I'm assuming the same issue will be happening with the month portion, although I've only seen it with the day portion. How would I take the elements of the cells array, and format them as dates with the format mm/dd/yyyy, with leading zeros if the month or day is a single digit.

The array will always be different, but elements 5, 6 and 7, will always need to be dates.

my array:

[1] [
    [0] "297",
    [1] "name",
    [2] "463",
    [3] "value",
    [4] "value1",
    [5] "12/8/2013",
    [6] "12/9/2013",
    [7] "12/9/2013"
],

Answer 1

要将您说的格式更改为mm/dd/yyyy ，请尝试以下操作：

sprintf("%02i/%02i/%4i", *(datestr.split("/").map {|i| i.to_i}))

Answer 2

If you want the strings converted to date objects:

require 'date'

cells = []
cells[5] = "12/8/2013"
cells[6] = "12/9/2013"
cells[7] = "12/9/2013"

(5..7).each do |i|
  cells[i] = Date.strptime(cells[i], '%m/%d/%Y')
  puts "#{cells[i]} (#{cells[i].class} object)"
end

Result:

2013-08-12 (Date object)
2013-09-12 (Date object)
2013-09-12 (Date object)

Answer 3

Assuming the array cells always has dates at index 5 through 7, the following will update the cells array to have the dates in mm/dd/yyyy format:

require 'date'

cells[5..7] = cells[5..7].map { |date| Date.parse(date).strftime('%m/%d/%Y') }

Answer 4

require 'date'

arr = ["297", "name", "463", "value", "value1", \
       "12/8/2013", "12/9/2013", "12/9/2013"]

FMT = '%m/%d/%Y'

arr.map! do |e|
  begin
    Date.strptime(e, FMT).strftime(FMT)
  rescue
    e
  end
end

arr # => ["297", "name", "463", "value", "value1", \
    #     "12/08/2013", "12/09/2013", "12/09/2013"]

I just allowed an exception to be raised by strptime when e does not represent a date with format FMT , in which case the corresponding element of arr is left unchanged. Alternatively, something like if e =~ /^\\d*\\/\\d*\\/(\\d*)$/... could be used.

One could instead use Date.parse(e).strftime(FMT) (as @OI did), because the m/d/y order is not changing, but I prefer strptime in this situation because it is more demanding of the required date format.

Answer 5

There could be parsing problems you're seeing that changing the format of the string won't fix at all. Consider this:

require 'date'

date = Date.parse("12/8/2013") # => #<Date: 2013-08-12 ((2456517j,0s,0n),+0s,2299161j)>
date.day # => 12

When Date tries to parse a date in this format, it assumes something that is unintuitive to Americans, but makes sense to the rest of the world. In the US, we assume a date is in mm/dd/yyyy format. The "right-thinking" people around the rest of the world understand it means dd/mm/yyyy . Ruby, being oriented toward the rest of the world uses dd/mm/yyyy .

To fix that we have to be a bit smarter about how we parse a date, and actually tell Date what to use:

date = Date.strptime("12/8/2013", '%d/%m/%Y') # => #<Date: 2013-08-12 ((2456517j,0s,0n),+0s,2299161j)>
date.day # => 12

Or:

date = Date.strptime("12/8/2013", '%m/%d/%Y') # => #<Date: 2013-12-08 ((2456635j,0s,0n),+0s,2299161j)>
date.day # => 8

If all you want to do is add zero-filled fields, you can do that several ways:

array = [
  "297",
  "name",
  "463",
  "value",
  "value1",
  "12/8/2013",
  "12/9/2013",
  "12/9/2013"
].map { |e|

  if e[%r=(\d+)/(\d+)/(\d+)=]
    '%02d/%02d/%04d' % [$1, $2, $3]
  else
    e
  end

}
array # => ["297", "name", "463", "value", "value1", "12/08/2013", "12/09/2013", "12/09/2013"]

Or using a ternary statement for more obscurity:

array = [
  "297",
  "name",
  "463",
  "value",
  "value1",
  "12/8/2013",
  "12/9/2013",
  "12/9/2013"
].map { |e|

  e[%r=(\d+)/(\d+)/(\d+)=] ? '%02d/%02d/%04d' % [$1, $2, $3] : e

}
array # => ["297", "name", "463", "value", "value1", "12/08/2013", "12/09/2013", "12/09/2013"]

If you want to reverse the fields:

array = [
  "297",
  "name",
  "463",
  "value",
  "value1",
  "12/8/2013",
  "12/9/2013",
  "12/9/2013"
].map { |e|

  if e[%r=(\d+)/(\d+)/(\d+)=]
    '%02d/%02d/%04d' % [$2, $1, $3]
  else
    e
  end

}
array # => ["297", "name", "463", "value", "value1", "08/12/2013", "09/12/2013", "09/12/2013"]

Or use the ternary line with the search results swapped.

Or use scan :

array = [
  "297",
  "name",
  "463",
  "value",
  "value1",
  "12/8/2013",
  "12/9/2013",
  "12/9/2013"
].map { |e|

  numerics = e.scan(/\d+/)
  case numerics.size
  when 3
    '%02d/%02d/%04d' % numerics
  else
    e
  end

}
array # => ["297", "name", "463", "value", "value1", "12/08/2013", "12/09/2013", "12/09/2013"]

And if you want to reverse the fields:

'%02d/%02d/%04d' % [numerics[1], numerics[0], numerics[2]]

Which to use depends on whatever you mean by "causing issues".