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 Xah Lee 03-22-2005 05:02 PM

[perl-python] sorting matrixes

Today we'll write a program that can sort a matrix in all possible
ways.

Here's the Perl documentation. I'll post a Perl and Python version in 2
days.

-----------

sort_matrix( \$matrix, [[\$n1, \$stringQ, \$directionQ], [\$n2, \$stringQ,
\$directionQ], ...]) sorts a matrix by \$n1 th column then \$n2 th...and
so on.

\$matrix must be a reference to references of arrays, having the form
[[\$e1, \$e2,...], [...], ...]. \$stringQ is a boolean indicating
whether to treat corresponding columns as a strings instead of as
number in the sorting process. True means string. \$directionQ is a
boolean indicating ascending sort or not for the correpsonding
column. In the column spec \$n1 \$n2 ..., index counting starts at 0.

Example:

my \$ref_matrix =
[
[3, 99, 'a'],
[2, 77, 'a'],
[1, 77, 'a']
];

sort_matrix( \$ref_matrix, [ [2,1,1], [1,0,1] ]);
# this means sort by third column, regarding it as strings,
# and in ascending order. If tie, sort by second column,
# regarding it as number, in ascending order.

# returns [[2,77,'a'],[1,77,'a'],[3,99,'a']];

------------------

Note: in the above, ignore the "must be a reference to references of
arrays". That's technical point, because Perl the language do nested
lists thru workaround of "references".

http://xahlee.org/perl-python/sort_matrix.html

 Christos TZOTZIOY Georgiou 03-22-2005 06:19 PM

Re: [perl-python] sorting matrixes

On 22 Mar 2005 09:02:51 -0800, rumours say that "Xah Lee" <xah@xahlee.org> might
have written:

>Today we'll write a program that can sort a matrix in all possible
>ways.
>
>Here's the Perl documentation. I'll post a Perl and Python version in 2
>days.

Don't bother writing a Python version... list.sort and its arguments are fine
and send their greetings.
--
TZOTZIOY, I speak England very best.
"Be strict when sending and tolerant when receiving." (from RFC1958)
I really should keep that in mind when talking with people, actually...

 Xah Lee 03-28-2005 04:24 AM

Re: sorting matrixes

Here's the solution to previous post.

-------------------------------
perl code:

sub sort_matrix(\$\$) {
my \$ref_matrix = \$_[0];
my @indexMatrix = @{\$_[1]};

my @indexes = map {\$_->[0]} @indexMatrix;
my @operators = map {\$_->[1] ? ' cmp ' : ' <=> '} @indexMatrix;
my @directions = map {\$_->[2]} @indexMatrix;

my \$body_code = '';
my @body_array;
for (my \$i = 0; \$i <= \$#indexes; \$i++) {
if (\$directions[\$i]) {
push(@body_array, "(\\$a->[\$i]" . \$operators[\$i] .
"\\$b->[\$i])");
} else {
push(@body_array, "(\\$b->[\$i]" . \$operators[\$i] .
"\\$a->[\$i])");
};
};
\$body_code = join( ' or ', @body_array);

my \$array_code = '(map { [' . join(q(, ), map {"\\$_->[\$_]"}
@indexes) . ', \$_]} @\$ref_matrix)';

my \$code = "map {\\$_->[-1]} (sort { \$body_code} \$array_code)";
my @result = eval \$code;
return [@result];
};

------------------------------------------
Python code

# python v 2.4

def sort_matrix(matrix, directives):
result=matrix
for dir in directives:
if dir[1]:
if dir[2]:
result.sort(lambda x,y: cmp( str(x[dir[0]]),
str(y[dir[0]])) )
else:
result.sort(lambda x,y: cmp( str(x[dir[0]]),
str(y[dir[0]])), None, True)
else:
if dir[2]:
result.sort(lambda x,y: cmp(float(x[dir[0]]),
float(y[dir[0]])) )
else:
result.sort(lambda x,y: cmp(float(x[dir[0]]),
float(y[dir[0]])), None, True )
return result

m = [
[3, 99, 'a'],
[2, 77, 'a'],
[1, 77, 'a']
]

print sort_matrix(m,[
[2,True,True],
[1,False,True]
])

The Python code has not been tested much.

http://xahlee.org/perl-python/sort_matrix.html

Xah
xah@xahlee.org
http://xahlee.org/PageTwo_dir/more.html

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