Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>It appears there is no built-in string formatting trick which allows you to (1) print floats whose first significant digit appears after the 15th decimal place and (2) not in scientific notation. So that leaves manual string manipulation.</p> <p>Below I use the <code>decimal</code> module to extract the decimal digits from the float. The <code>float_to_decimal</code> function is used to convert the float to a <code>Decimal</code> object. The obvious way <code>decimal.Decimal(str(f))</code> is wrong because <code>str(f)</code> can lose significant digits.</p> <p><code>float_to_decimal</code> was lifted from the <a href="http://docs.python.org/library/decimal.html#decimal-faq" rel="nofollow noreferrer">decimal module's documentation</a>.</p> <p>Once the decimal digits are obtained as a tuple of ints, the code below does the obvious thing: chop off the desired number of sigificant digits, round up if necessary, join the digits together into a string, tack on a sign, place a decimal point and zeros to the left or right as appropriate. </p> <p>At the bottom you'll find a few cases I used to test the <code>f</code> function.</p> <pre><code>import decimal def float_to_decimal(f): # http://docs.python.org/library/decimal.html#decimal-faq "Convert a floating point number to a Decimal with no loss of information" n, d = f.as_integer_ratio() numerator, denominator = decimal.Decimal(n), decimal.Decimal(d) ctx = decimal.Context(prec=60) result = ctx.divide(numerator, denominator) while ctx.flags[decimal.Inexact]: ctx.flags[decimal.Inexact] = False ctx.prec *= 2 result = ctx.divide(numerator, denominator) return result def f(number, sigfig): # http://stackoverflow.com/questions/2663612/nicely-representing-a-floating-point-number-in-python/2663623#2663623 assert(sigfig&gt;0) try: d=decimal.Decimal(number) except TypeError: d=float_to_decimal(float(number)) sign,digits,exponent=d.as_tuple() if len(digits) &lt; sigfig: digits = list(digits) digits.extend([0] * (sigfig - len(digits))) shift=d.adjusted() result=int(''.join(map(str,digits[:sigfig]))) # Round the result if len(digits)&gt;sigfig and digits[sigfig]&gt;=5: result+=1 result=list(str(result)) # Rounding can change the length of result # If so, adjust shift shift+=len(result)-sigfig # reset len of result to sigfig result=result[:sigfig] if shift &gt;= sigfig-1: # Tack more zeros on the end result+=['0']*(shift-sigfig+1) elif 0&lt;=shift: # Place the decimal point in between digits result.insert(shift+1,'.') else: # Tack zeros on the front assert(shift&lt;0) result=['0.']+['0']*(-shift-1)+result if sign: result.insert(0,'-') return ''.join(result) if __name__=='__main__': tests=[ (0.1, 1, '0.1'), (0.0000000000368568, 2,'0.000000000037'), (0.00000000000000000000368568, 2,'0.0000000000000000000037'), (756867, 3, '757000'), (-756867, 3, '-757000'), (-756867, 1, '-800000'), (0.0999999999999,1,'0.1'), (0.00999999999999,1,'0.01'), (0.00999999999999,2,'0.010'), (0.0099,2,'0.0099'), (1.999999999999,1,'2'), (1.999999999999,2,'2.0'), (34500000000000000000000, 17, '34500000000000000000000'), ('34500000000000000000000', 17, '34500000000000000000000'), (756867, 7, '756867.0'), ] for number,sigfig,answer in tests: try: result=f(number,sigfig) assert(result==answer) print(result) except AssertionError: print('Error',number,sigfig,result,answer) </code></pre>
    singulars
    1. This table or related slice is empty.
    1. PONicely representing a floating-point number in python
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USunutbu
    1. USunutbu
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PONicely representing a floating-point number in python
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUndeletion
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COThat's some beautiful code. It's exactly what I wanted. If you change it so that it takes a Decimal instead of float (which is trivial to do), then we can avoid floating-point errors all together. The only problem I find is with long integers. For example, try `(34500000000000000000000, 17, '34500000000000000000000')`. Though, again, this is probably just from floating-point errors.
      singulars
      1. PO
      1. USdln385
    2. COGood catch. I made a slight change to the definition of `d` which fixes the problem with long ints, and as a side-effect, allows you to also pass numeric strings for the `number` arg as well.
      singulars
      1. PO
      1. USunutbu
    3. COThat fix works, but I found other, unrelated errors. Using `(756867, 7, '756867.0')`, I get back `75686.7`. It seems the conditions for padding the result are a little off.
      singulars
      1. PO
      1. USdln385
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload