[英]Rounding towards zero on a PDL
我有一個混合值(正數和負數)的PDL(類型double
)。 我想將每個條目四舍五入。 所以+1.2
變為+1
, +1.7
變為+1
, -1.2
變為-1
和-1.7
變為-1
,
我考慮過使用int()
,但是它不適用於PDL類型。
我還可以使用round(abs($x) - 0.5) * ($x <=> 0)
,但不確定如何在PDL上使用此邏輯。
指針?
PDL :: Math中的rint
函數的文檔說:
如果要將半整數從零舍入,請嘗試
floor(abs($x)+0.5)*($x<=>0)
。
只需對其稍作更改即可使其按您想要的方式工作:
#!/usr/bin/perl
use warnings;
use strict;
use PDL;
my $pdl = 'PDL'->new(
[ 1, 1.3, 1.9, 2, 2.1, 2.7 ],
[ -1, -1.3, -1.9, -2, -2.1, -2.7 ]
);
$pdl = floor(abs($pdl)) * ($pdl <=> 0);
print $pdl;
輸出:
[
[ 1 1 1 2 2 2]
[-1 -1 -1 -2 -2 -2]
]
PDL :: Math有floor
, ceil
和rint
。 所有這些功能都就位。
因此,應執行以下操作:
#!/usr/bin/env perl
use warnings;
use strict;
use PDL;
my $pdl = 'PDL'->new(
[ 1, 1.3, 1.9, 2, 2.1, 2.7 ],
[ -1, -1.3, -1.9, -2, -2.1, -2.7 ]
);
print $pdl;
floor(inplace $pdl->where($pdl >= 0));
ceil (inplace $pdl->where($pdl < 0));
print $pdl;
輸出:
[
[ 1 1.3 1.9 2 2.1 2.7]
[ -1 -1.3 -1.9 -2 -2.1 -2.7]
]
[
[ 1 1 1 2 2 2]
[-1 -1 -1 -2 -2 -2]
]
PS:@choroba的答案在較舊的MacBook Pro上使用無線程 perl
5.24的以下基准測試中運行速度提高了約20%:
#!/usr/bin/env perl
use warnings;
use strict;
use constant N_ELEMS => $ARGV[0] || 100_000;
use Dumbbench;
use PDL;
sub one_scan {
my $pdl = 100 * grandom(N_ELEMS);
$pdl = floor(abs($pdl)) * ($pdl <=> 0);
return;
}
sub two_scans {
my $pdl = 100 * grandom(N_ELEMS);
floor(inplace $pdl->where($pdl >= 0));
ceil (inplace $pdl->where($pdl < 0));
return;
}
sub baseline {
my $pdl = 100 * grandom(N_ELEMS);
return;
}
my $bench = Dumbbench->new;
$bench->add_instances(
Dumbbench::Instance::PerlSub->new(code => \&baseline, name => 'Baseline'),
Dumbbench::Instance::PerlSub->new(code => \&one_scan, name => 'One Scan'),
Dumbbench::Instance::PerlSub->new(code => \&two_scans, name => 'Two Scans'),
);
$bench->run;
$bench->report;
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