I've got a plist (created in XCode) with an array full of "Numbers" (0.01, 1, 2, 6) that unpacks into NSValues when reconstituted with initWithContentsOfFile. How can I turn these NSValues into NSDecimalNumbers that I can use for adding together? They will be treated as currency values so only need precision of 2 (maybe 4) decimal places.
I've tried saving the plist values as "String" instead of "Number" and using NSDecimalNumber's initWithString to set the value but then NSValue doesn't respond to stringValue.
Seems like dealing with numbers is particularly confusing in Cocoa. so many container formats in so many frameworks... :-(
You should be able to directly store your numbers as strings in the property list. You don't need to do any NSValue wrapping for NSStrings when storing them in a plist. I'd recommend keeping the numbers in your application as NSDecimals or NSDecimalNumbers to avoid any floating-point errors, reading them from the plist using initWithString:locale:, and writing them to the plist using descriptionWithLocale:. Storing and retrieving the decimals as strings avoids any to-and-from floating point conversion errors.
The first lesson to learn is that when representing currency, use integers instead of floating-point (decimal) numbers if you want any kind of accuracy. (Divide by 100.0 whenever you need to display cents, etc.) Computers are flawless with binary (base 2) but if you try to represent in binary something that can't be broken down into factors of 1/(2^n), you'll run into precision errors. (Try 0.1 + 0.1 and see what you get.)
That said, the XML tag within which you specify the number definitely makes a difference in how the values are interpreted in terms of Cocoa classes when you use something like -[NSArray initWithContentsOfFile:] to "reconstitute" it. Consult the plist man page and this Apple article for more details and examples.
To accomplish what you're asking, make sure you're using <real> or <integer> (and the matching closing tag) around the values in your plist. (Property List Editor and Xcode should automatically use the correct one based on whether the number has a decimal point.) In my tests, both real and integer numbers were read in as NSNumber objects. NSDecimalNumber is a subclass of NSNumber, but I'm not entirely sure how the toll-free bridging with CFNumber works in all cases. Experimentation is probably the best way to figure that out.
Related
I know gdb has several means of exploring data, some of them quite convenient. However, I cannot combine them to get that I need/want. I would like to display some custom string based on the first n values of a big array starting at <PT_arr>, and the last m values of the same array at a distance (in this case) 4096. Looking something like this:
table beginning:
0x804cfe0 <PT_arr>: 0x00100300 0x00200300 0x00300300 0x00400300
table end:
0x804cfe0 <PT_arr+4064>: 0x00500300 0x00600300 0x00700300 0x00800300
printf let's me add custom text (like table beginning)
the examine x gives me that nice alignment, let's me read many elements and group them by byte, words, etc; and shows addresses at the left (which is ideal for my case).
x aligns the content of regions of memory in an easy to read manner with the size and unit parameters. (what I want)
display is constantly printing. (what I want).
The issue with display (manual), is that unlike examine x (manual) it doesn't have a size or unit parameter.
Is there a way to accomplish that?
Thanks.
I'm sort of new to Web2py. I have a system that's working just fine, but I want to make an improvement regarding visualization. There's a couple of fields that use numbers (defined as double in their respective define_table methods) to represent currency, but I want them to also show with a separator for thousands, such as 183,403,293.34. I checked some documentation, but I couldn't find a direct way to handle this form of customization, though I could be missing something.
Any suggestions regarding this? Cheers!
First, if representing currency, you should use the decimal field type rather than double (some calculations using double values may yield incorrect results due to the use of floating point representations internally). However, if using SQLite, there is no distinction between decimal and double, so in that case, you might want to multiply all values by 100 and instead store integers.
In any case, to display a given numeric value with thousands separators in Python, you can do:
'{:,}'.format(myvalue)
For more details, see https://stackoverflow.com/a/10742904/440323 and https://stackoverflow.com/a/21208495/440323.
If you are using the values via web2py functionality that makes use of the field's represent function (e.g., the grid or the .render() method), you can define a custom represent function, such as:
Field('amount', 'decimal(12, 2)',
represent=lambda v, r: '{:,}'.format(v) if v is not None else '')
You could use the Python function of the locale module:
{{= locale.format ('%. 2f', your_value, grouping = True)}}
Can I determine if the user entered a phone number that can be safely formatted into E164?
For Germany, this requires that the user started his entry with a local area code. For example, 123456 may be a subscriber number in his city, but it cannot be formatted into E164, because we don't know his local area code. Then I would like to keep the entry as it is. In contrast, the input 089123456 is independent of the area code and could be formatted into E164, because we know he's from Germany and we could convert this into +4989123456.
You can simply convert your number into E164 using libphonenumber
and after conversion checks if both the strings are same or not. If they're same means a number can not be formatted, otherwise the number you'll get from library will be formatted in E164.
Here's how you can convert
PhoneNumberUtil phoneUtil = PhoneNumberUtil.getInstance();
String formattedNumber = phoneUtil.format(inputNumber, PhoneNumberFormat.E164);
Finally compare formattedNumber with inputNumber
It looks as though you'll need to play with isValidNumber and isPossibleNumber for your case. format is certainly not guaranteed to give you something actually dialable, see the javadocs. This is suggested by the demo as well, where formatting is not displayed when isValidNumber is false.
I also am dealing with this FWIW. In the context of US numbers: The issue is I'd like to parse using isPossibleNumber in order to be as lenient as possible, and store the number in E164. However then we accept, e.g. +15551212. This string itself even passes isPossibleNumber despite clearly (I think) not being dialable anywhere.
In google's Protocol Buffers, I use large enums and I have to assign each integer value explicitly:
enum Function {ProcessLibrary=0;
RotateLeft=1;
RotateRight=2;
...}
This is very annoying and ugly. Is there a way to avoid these integer values in the code?
something like:
enum Function {ProcessLibrary;
RotateLeft;
RotateRight;
...}
No, basically. This is deliberate to prevent huge errors when adding / removing enums, and to allow for non-contiguous enums.
In most real-world cases where the list of names is already defined elsewhere, you can write a 5 line script to add =n onto each - heck, a spreadsheet calculation and "fill down" would go a long way to it - paste names into the first column, copy the generated lines out of the second.
I'm trying to generate UUIDs with the same style as bit.ly urls like:
http://bit [dot] ly/aUekJP
or cloudapp ones:
http://cl [dot] ly/1hVU
which are even smaller
how can I do it?
I'm now using UUID gem for ruby but I'm not sure if it's possible to limitate the length and get something like this.
I am currently using this:
UUID.generate.split("-")[0] => b9386070
But I would like to have even smaller and knowing that it will be unique.
Any help would be pretty much appreciated :)
edit note: replaced dot letters with [dot] for workaround of banned short link
You are confusing two different things here. A UUID is a universally unique identifier. It has a very high probability of being unique even if millions of them were being created all over the world at the same time. It is generally displayed as a 36 digit string. You can not chop off the first 8 characters and expect it to be unique.
Bitly, tinyurl et-al store links and generate a short code to represent that link. They do not reconstruct the URL from the code they look it up in a data-store and return the corresponding URL. These are not UUIDS.
Without knowing your application it is hard to advise on what method you should use, however you could store whatever you are pointing at in a data-store with a numeric key and then rebase the key to base32 using the 10 digits and 22 lowercase letters, perhaps avoiding the obvious typo problems like 'o' 'i' 'l' etc
EDIT
On further investigation there is a Ruby base32 gem available that implements Douglas Crockford's Base 32 implementation
A 5 character Base32 string can represent over 33 million integers and a 6 digit string over a billion.
If you are working with numbers, you can use the built in ruby methods
6175601989.to_s(30)
=> "8e45ttj"
to go back
"8e45ttj".to_i(30)
=>6175601989
So you don't have to store anything, you can always decode an incoming short_code.
This works ok for proof of concept, but you aren't able to avoid ambiguous characters like: 1lji0o. If you are just looking to use the code to obfuscate database record IDs, this will work fine. In general, short codes are supposed to be easy to remember and transfer from one medium to another, like reading it on someone's presentation slide, or hearing it over the phone. If you need to avoid characters that are hard to read or hard to 'hear', you might need to switch to a process where you generate an acceptable code, and store it.
I found this to be short and reliable:
def create_uuid(prefix=nil)
time = (Time.now.to_f * 10_000_000).to_i
jitter = rand(10_000_000)
key = "#{jitter}#{time}".to_i.to_s(36)
[prefix, key].compact.join('_')
end
This spits out unique keys that look like this: '3qaishe3gpp07w2m'
Reduce the 'jitter' size to reduce the key size.
Caveat:
This is not guaranteed unique (use SecureRandom.uuid for that), but it is highly reliable:
10_000_000.times.map {create_uuid}.uniq.length == 10_000_000
The only way to guarantee uniqueness is to keep a global count and increment it for each use: 0000, 0001, etc.