I'm trying to make an api endpoint to output BigDecimal numbers as "numbers" in JSON. HighCharts requires any numeral value to be a number instead of a string. But I couldn't make a JSON object with the BigDecimal numbers shown as real numbers, not strings or anything else.
I need to generate something like this:
[[123000, 235436.352642],[127000, 9434.2352663], ... ]
There are many answers to this question on the web like this, but all of them suggest to convert the BigDecimal to Float via .to_f. And that, doesn't make any sense, cause we use decimals to have an exact precision which is not the case with Float.
You could "round" those numbers, to "numbers"
v = BigDecimal("7.176231231231231")
sprintf("%.6f", v)
# => "7.176231"
And you could also string truncate onto the function to get more specific, rounded numbers(might be useful when using this data for graphs).
v = BigDecimal("7.176231231231231")
sprintf("%.6f", v)
# => "7.176231"
sprintf("%.6f", v.truncate(2))
# => "7.170000"
Related
I have a list of float numbers, representing currency, and I need to turn them into integers, for precision.
The task is to turn float numbers into integers, likes:
0.95 => 95
1 => 100
1,465.01 => 146501
The problem is:
I don't have access to change the input csv files
The numbers came in a variety of ways (1.00, 1.0, 1, .95, 0.95, etc)
How can, safely, I turn these numbers into integers?
Some examples of my problem:
('16.81'.to_f * 100).to_i => 1680
('16.81'.to_f * 100_00).to_i / 100 => 1681
('342.28'.to_f * 100).to_i => 34228
('342.28'.to_f * 100_00).to_i / 100 => 34227
__ EDIT __
By the way, I'm using ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-darwin19]
Floating point numbers can't necessarily represent all decimal numbers. This is explained in Is floating point math broken?. As such, when dealing with floats, you are always a bit uncertain and usually need to use rounding to get a desired number.
From your examples, ('16.81'.to_f * 100) results in 1680.9999999999998. Getting the integer value from that cuts off the fractional part, resulting in 1680. By using round instead, you can get the desired integer (which also solves the issue of partial cents). When relying on this, please note the details of how Ruby rounds exactly, specifically the optional half argument).
Instead of relying on Floats however, a better idea is to use BigDecimal numbers instead which allow arbitrary precision floating point numbers.
require 'bigdecimal'
(BigDecimal('16.81') * 100).round
# => 1681
(BigDecimal('.95') * 100).round
# => 95
number = '1,465.01'
# remove any "additional" characters
normalized = number.gsub(/[^-+0-9.]/, '')
(BigDecimal(normalized) * 100).round
# => 146501
In the last example, I have shown how you might cleanup your "human-readable" numbers for consistent parsing. Depending on your source data, you might need to perform additional changes (e.g. if you might have values such as '1.465,01' as is common in e.g. some European countries).
Use Bigdecimal for float numbers and append .to_i to convert it in integer
require 'bigdecimal'
(BigDecimal('16.81') * 100).to_i # 1681
(BigDecimal('342.28') * 100).to_i # 34228
For more details you can refer https://corainchicago.github.io/blog/why-does-ruby-add-numbers-wrong/
Scribunto is a MediaWiki-hosted version of Lua.
I believe it is fairly standard Lua.
I want to convert geographic coordinates from this format:
42°33'N, 1°33'E
... to this format:
42.55|1.55
How to do this in Scribunto?
This assumes the input string is strictly of the form in the post. If there's any variability e.g. it can omit the minutes, include seconds, latitude and longitude can be separated differently, or whatever, the pattern will need to change.
function translate_coords(str)
assert(type(str)=="string")
local patt = "(%d+)°(%d+)'([NS]), (%d+)°(%d+)'([WE])"
local latd,latm,latdir,lngd,lngm,lngdir = string.match(str,patt)
assert(latd and latm and latdir)
assert(lngd and lngm and lngdir)
latd = latdir=="S" and -latd or latd
lngd = lngdir=="W" and -lngd or lngd
return ""..(latd+latm/60).."|"..(lngd+lngm/60)
end
I have an array in Ruby which has values as follows
xs = %w(2.0.0.1
2.0.0.6
2.0.1.10
2.0.1.5
2.0.0.8)
and so on. I want to sort the array such that the final result should be something like this :
ys = %w(2.0.0.1
2.0.0.6
2.0.0.8
2.0.1.5
2.0.1.10)
I have tried using the array.sort function, but it places "2.0.1.10" before "2.0.1.5". I am not sure why that happens
Using a Schwartzian transform (Enumerable#sort_by), and taking advantage of the lexicographical order defined by an array of integers (Array#<=>):
sorted_ips = ips.sort_by { |ip| ip.split(".").map(&:to_i) }
Can you please explain a bit more elaborately
You cannot compare strings containing numbers: "2" > "1", yes, but "11" < "2" because strings are compared lexicographically, like words in a dictionary. Therefore, you must convert the ip into something than can be compared (array of integers): ip.split(".").map(&:to_i). For example "1.2.10.3" is converted to [1, 2, 10, 3]. Let's call this transformation f.
You could now use Enumerable#sort: ips.sort { |ip1, ip2| f(ip1) <=> f(ip2) }, but check always if the higher abstraction Enumerable#sort_by can be used instead. In this case: ips.sort_by { |ip| f(ip) }. You can read it as "take the ips and sort them by the order defined by the f mapping".
Split your data into chunks by splitting on '.'. There is no standard function to do it as such so you need to write a custom sort to perform this.
And the behaviour you said about 2.0.1.10 before 2.0.1.5 is expected because it is taking the data as strings and doing ASCII comparisons, leading to the result that you see.
arr1 = "2.0.0.1".split('.')
arr2 = "2.0.0.6".split('.')
Compare both arr1 and arr2 element by element, for all the data in your input.
Easy question here, probably, but searching did not find a similar question.
The # operator finds the length of a string, among other things, great. But with Lua being dynamically typed, thus no conversion operators, how does one type a number as a string in order to determine its length?
For example suppose I want to print the factorials from 1 to 9 in a formatted table.
i,F = 1,1
while i<10 do
print(i.."! == "..string.rep("0",10-#F)..F)
i=i+1
F=F*i
end
error: attempt to get length of global 'F' (a number value)
why not use tostring(F) to convert F to a string?
Alternatively,
length = math.floor(math.log10(number)+1)
Careful though, this will only work where n > 0!
There are probably a dozen ways to do this. The easy way is to use tostring as Dan mentions. You could also concatenate an empty string, e.g. F_str=""..F to get F_str as a string representation. But since you are trying to output a formatted string, use the string.format method to do all the hard work for you:
i,F = 1,1
while i<10 do
print(string.format("%01d! == %010d", i, F))
i=i+1
F=F*i
end
Isn't while tostring(F).len < 10 do useful?
I am storing a cost in my application. The cost is not formatted in the database. For example: 00.00 saves as 0, 1.00 saves as 1, and 40.50 saves as 40.5
I need to read these values from the database and convert them to strings for dollars and cents. For example: 0 --> cost_dollars = "00" & cost_cents = "00", 1 --> cost_dollars = "01" & cost_cents = "00", 40.5 --> cost_dollars = "40" & cost_cents = "50".
Is there an easy way to do this in ruby on rails? Or does someone have code that does this?
Thanks!
You can accomplish that with this little bit of Ruby code:
fmt = "%05.2f" % cost
cost_dollars, cost_cents = fmt.split '.'
If you're trying to format dollar values in a view, you should look at number_to_currency in ActionView::Helpers::NumberHelper.
>> bd = BigDecimal.new "5.75"
>> include ActionView::Helpers
>> number_to_currency(bd)
=> "$5.75"
As for breaking up the value into separate dollars and cents, my first question would be, "Why?" If you have a good reason, and you're dealing with decimals in your database, then you could do the following.
>> bd = BigDecimal.new "5.75"
>> "dollars:#{bd.truncate} cents:#{bd.modulo(1) * BigDecimal.new('100')}"
=> "dollars:5.0 cents:75.0"
number_to_currency is nice, but it can get expensive; you might want to roll your own if you need to call it a lot.
You should be aware that using a float to store currency can be problematic (and see) if you do a lot of calculations based on these values. One solution is to use integers for currency and count cents. This appears to be the approach used by the money plugin. Another solution is to use a decimal type in your migration, which should work out-of-the-box for modern versions of Rails (> 1.2):
add_column :items, :price, :decimal, :precision => 10, :scale => 2
(:scale is the number of places past the decimal, :precision is the total number of digits.) This will get you BigDecimal objects in Rails, which are a little harder to work with, but not too bad.
Both the integer and decimal approaches are a little slower than floating point. I'm using floats for currency in some places, because I know I won't need to do calculations on the values within Rails, only store and display them. But if you need accurate currency calculations, don't use floats.
Instead of storing as a decimal, store as an integral number of cents. So 1 dollar is stored as 100 in the database.
Alternatively, if you don't mind a bit of performance overhead, check for '.' in the database's value. If it exists, split on '.', and parse the pieces as integers.
sprintf is your friend here:
cost_dollars = sprintf('%02.f', cost)
cost_cents = sprintf('%.2f', cost)