Compare decimal representations of floating-point numbers.
A package to compare decimal representations of floating-point numbers, including a command-line tool to report on the similarity between data in CSV files.
comparedecimal package can be installed from source by running
pip3 install . or
python3 setup.py within its directory. The command-line
comparecsv will be installed as part of the package.
I wrote this tool to help me when organizing and tidying up scientific
data sets. It occasionally happens that I come across two files which I
suspect contain the same data, but because they've been through different
processing steps, the values are no longer byte-for-byte identical – for
example, a CSV file may have been opened in Excel and saved again,
truncating the number of decimal places in the floating-point values. In
these cases, it's useful to be able to ascertain how compatible the files
are – is it possible that one is a lower-precision version of the other
(e.g. ‘2.0’ and ‘1.99’)? Or that the numerical values are in fact
identical but the strings representing them differ (e.g. ‘1234’ and
comparedecimal provides a Python package and command-line
tool to answer such questions.
For any pair of strings,
comparedecimal determines one of five equality
levels between them. The highest possible equality level is always given,
so for instance a pair of strings which is both ‘compatible’ and ‘close’
will be classified as ‘compatible’. The equality levels are as follows:
Identical: the character strings are equal.
Numerically equal: the character strings, when parsed as floating-point decimals, produce numbers which are equal.
Compatible: there exists a single floating-point number which, when formatted, could produce both the string representations. Under this definition, for example, "1.9" and "1.95" would be compatible, because they are both valid representations of 1.949. This equality level is particularly useful for finding duplicate files with differing levels of precision.
Close: the difference between the numbers represented by the character strings is below a certain threshold (formally: denoting the represented values by
band the threshold by
t, they are close if have the same sign and
max(abs(a), abs(b)) <= (1 + t) * min(abs(a), abs(b))). This equality level is useful for finding ‘duplicate’ files generated from the same data in which truncation or rounding errors have caused values to diverge slightly.
Unequal: The character strings are unequal and cannot represent the same number, and the values they represent are not close in the sense defined above.
comparedecimal package provides the class
is initialized with a separator string (used to divide lines for multi-field
comparisons) and a threshold (used to define the
Close equality level
described above). The class provides the following methods:
compare_stringsto compare individual strings
compare_string_liststo compare lists of strings
compare_line_liststo compare lists of lines, using the predefined separator to split each line into strings
DecimalComparer has an instance variable
totals is a
dictionary with a key for each equality level (represented by the
EqualityLevel enum). The associated value for each equality level is
an integer representing the total number of comparisons made so far
which resulted in this equality level.
comparecsv command-line tool
comparecsv is a command line utility for finding duplicates among
delimited textual files containing numerical data (e.g. CSV files), even
when the string representations of the data differ.
comparecsv takes as its arguments two delimited files with the same
layout (i.e. same number of rows and columns) and compares them field by
field. For each pair of corresponding fields, it determines a level of
equality as defined above.
When run on two files,
comparecsv prints total counts for field pairs
at each level of equality. For every field pair, the highest possible
equality level is given: for instance, if two fields are not identical but
are numerically equal, then they will (by definition) also be compatible
and close; in this case,
comparecsv will report the equality level
Copyright 2018, 2019 Pontus Lurcock firstname.lastname@example.org
Released under the GNU GPL v3; see the file COPYING for details.
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