Perl 中 qw 和数学操作的作用
Role of qw and math manipulation in Perl
我不明白 qw 在 Perl 中的作用，这是我在调试此 中的代码时理解的。
它的手册非常有限 here: qw/string/.
我试图了解以下代码中出了什么问题我正在对数据进行简单操作（乘以一 (1.0)）。
原始代码是真实案例中情况的简化版本
use v5.16;
use Math::Geometry::Planar qw(SegmentLineIntersection);
sub x_intercepts {
my ($points) = @_;
die 'Must pass at least 2 points' unless @$points >= 2;
my @intercepts;
my @x_axis = ( [0, 2000], [1, 2000] );
foreach my $i (0 .. $#$points - 1) {
my $intersect = SegmentLineIntersection([@$points[$i,$i+1], @x_axis]);
push @intercepts, $intersect if $intersect;
}
return \@intercepts;
}
my @xs = qw/22.595451 20.089094 17.380813 15.091260 12.477935 10.054821 7.270003 4.804673 4.728526 4.619254 4.526920 4.418416 4.321419 4.219890 4.123336 4.009777 3.912648 3.804183 3.705847 3.597756 3.512301 3.393413 3.301963 3.196725 3.098560 3.007482 2.899825 2.801002 2.688680 2.598862 2.496139 2.393526 2.282183 2.190449 2.084530 1.987778 1.877562 1.788788 1.678473 1.578123 1.467071 1.373372 1.283629 1.176670 1.071805 0.975422 0.877622 0.767820 0.667409 0.562480 0.469068 0.354589 0.264291 0.152522 0.063765 -0.045323 -0.136783 -0.248559 -0.343694 -0.459178 -0.551917 -0.640803 -0.755502 -0.845535 -0.955227 -1.045879 -1.155600 -1.254556 -1.365163 -1.461669 -1.571370 -1.658043 -1.772672 -1.865942 -1.981037 -2.073702 -2.176205 -2.276184 -2.367371 -2.476278 -2.567385 -2.686326 -2.777433 -2.884357 -2.980067 -3.087754 -3.183607 -3.291003 -3.386942 -3.495822 -3.586759 -3.702955 -3.793550 -3.900680 -3.999672 -4.093094 -4.200047 -4.301026 -4.399742 -4.493190 -4.602013 -4.705124 -4.812383 -4.907510 -5.022904 -5.109829 -5.214304 -5.317662 -7.703172 -10.350131 -12.921361 -15.431203 -18.188013 -20.544248 -22.822808 -25.679854 -22.999092 -20.540434 -17.964916 -15.398857 -12.990375 -10.402209 -7.888263 -5.504909 -5.217892 -5.109841 -5.014187 -4.908558 -4.811807 -4.704282 -4.605555 -4.504613 -4.406546 -4.292540 -4.204043 -4.088770 -3.995524 -3.905669 -3.796544 -3.707958 -3.596449 -3.490966 -3.382869 -3.293054 -3.185821 -3.088417 -2.971214 -2.880314 -2.772518 -2.677986 -2.569794 -2.473668 -2.365096 -2.276422 -2.179232 -2.068195 -1.973110 -1.859565 -1.771873 -1.669422 -1.569953 -1.462626 -1.364911 -1.258100 -1.159318 -1.050486 -0.959979 -0.849149 -0.749421 -0.640950 -0.547122 -0.451754 -0.344463 -0.252269 -0.134625 -0.051640 0.052970 0.154112 0.266505 0.353926 0.468739 0.561666 0.673810 0.759169 0.881697 0.973207 1.082409 1.170424 1.282163 1.378096 1.472728 1.586454 1.678473 1.785688 1.873862 1.984090 2.086021 2.196799 2.292400 2.386097 2.493190 2.601726 2.694346 2.803450 2.901878 3.011959 3.103050 3.196979 3.294507 3.397563 3.504076 3.600163 3.712539 3.809573 3.919799 4.012314 4.120694 4.216406 4.322895 4.416466 4.522871 4.623917 4.735925 4.826929 7.361253 9.647208 12.337984 14.870260 17.439730 19.921717 22.524080 25.125903/;
# -1 1.0 3 4 5 6 7 7 8 9 10/;
my @ys = qw/3699.316162 3676.939697 3659.950195 3641.476318 3605.965576 3580.152588 3555.092529 3528.118408 3509.595703 3504.416504 3508.355957 3510.452881 3510.304443 3499.548340 3499.943848 3493.196533 3499.488770 3494.984375 3494.390137 3493.938965 3492.606689 3493.434814 3488.926514 3488.890869 3484.599854 3488.077393 3484.177979 3477.801758 3478.098877 3472.040039 3477.642090 3477.802002 3472.908447 3478.532715 3469.805420 3472.759766 3464.269043 3463.950684 3465.888184 3458.441650 3459.006104 3455.686035 3455.677490 3454.548828 3454.241211 3455.250000 3449.803711 3447.423340 3457.498779 3448.445557 3453.106689 3447.701172 3444.543945 3448.558350 3450.073730 3449.884033 3444.751953 3444.056152 3444.825195 3449.671143 2593.656494 788.985779 776.407776 776.385925 767.522522 774.794250 770.596008 775.218384 770.962769 766.214294 766.735962 759.847351 760.073486 760.026489 753.721741 755.601929 753.942566 758.356506 747.932617 746.332214 746.464844 747.055115 750.173706 737.463379 739.810486 742.011475 744.332581 743.022461 737.302490 737.396606 734.325256 737.305359 740.642395 734.709717 735.754089 737.961182 740.697510 727.310913 730.918640 728.325012 721.845459 728.389893 727.765625 729.961243 725.608459 723.581909 730.736084 720.707764 720.398193 691.499390 657.534546 628.854431 615.219727 572.711365 561.505127 539.865173 517.139709 545.076416 580.880005 602.851135 628.006104 657.119263 683.746033 692.044373 716.640320 715.451294 715.415405 718.968018 723.698669 729.758606 728.564514 734.523376 731.454468 736.899780 731.257263 729.390686 732.837463 730.479431 733.497803 735.362732 742.581543 742.998108 735.918579 738.190002 738.108337 738.154297 740.425537 739.496033 743.105835 737.412537 740.537354 747.498108 747.424194 748.992920 752.244263 755.603455 756.611755 761.916504 762.920715 752.261658 758.293823 755.664062 753.728882 756.746338 754.825684 755.080444 761.192383 761.955505 763.209351 760.402771 764.342224 775.400940 767.148621 775.184998 777.084595 778.357117 776.217163 1086.248291 3444.476807 3438.105957 3440.625000 3438.325195 3438.430420 3449.251709 3453.216309 3452.126465 3458.547119 3451.694336 3456.417725 3457.336426 3457.777832 3455.553955 3457.256348 3458.823486 3459.088623 3459.492187 3463.538818 3466.455078 3456.521240 3459.809082 3457.505127 3462.721191 3466.518066 3467.562744 3469.211182 3469.120361 3464.043945 3466.291992 3472.698486 3476.146729 3471.635254 3472.539551 3475.163574 3473.687744 3479.102051 3488.351807 3482.367432 3481.961914 3484.844238 3481.511719 3482.469238 3488.947021 3488.882080 3491.247314 3499.116699 3511.889893 3539.602783 3565.981445 3598.203613 3628.028076 3657.928955 3685.231689/;
# my @ys = 1.0 * @ys;
my @input_list ;
foreach my $i ( 0..$#ys ) {
push @input_list, [ $xs[$i], $ys[$i] ] ;
}
my $intercept_list = x_intercepts(\@input_list) ;
say join ",", @$_ for @$intercept_list ;
我只是通过注释掉
来激活这一行 # my @ys = 1.0 * @ys;
Must pass at least 2 points at test2.pl line 7.
这表明 1.0 * qw_stuff 正在做一些超出我预期的事情。
我运行
my @ys = 1 * scalar(@ys); my @ys = qw/@ys/;
但同样的错误仍然存在。
如何在 Perl 中对整数和 qw 之间的数据进行简单的操作？
引用词：
my @xs = qw/22.595451 20.089094 17.380813 15.091260 12.477935 10.054821 7.270003 4.804673 4.728526 4.619254 4.526920 4.418416 4.321419 4.219890 4.123336 4.009777 3.912648 3.804183 3.705847 3.597756 3.512301 3.393413 3.301963 3.196725 3.098560 3.007482 2.899825 2.801002 2.688680 2.598862 2.496139 2.393526 2.282183 2.190449 2.084530 1.987778 1.877562 1.788788 1.678473 1.578123 1.467071 1.373372 1.283629 1.176670 1.071805 0.975422 0.877622 0.767820 0.667409 0.562480 0.469068 0.354589 0.264291 0.152522 0.063765 -0.045323 -0.136783 -0.248559 -0.343694 -0.459178 -0.551917 -0.640803 -0.755502 -0.845535 -0.955227 -1.045879 -1.155600 -1.254556 -1.365163 -1.461669 -1.571370 -1.658043 -1.772672 -1.865942 -1.981037 -2.073702 -2.176205 -2.276184 -2.367371 -2.476278 -2.567385 -2.686326 -2.777433 -2.884357 -2.980067 -3.087754 -3.183607 -3.291003 -3.386942 -3.495822 -3.586759 -3.702955 -3.793550 -3.900680 -3.999672 -4.093094 -4.200047 -4.301026 -4.399742 -4.493190 -4.602013 -4.705124 -4.812383 -4.907510 -5.022904 -5.109829 -5.214304 -5.317662 -7.703172 -10.350131 -12.921361 -15.431203 -18.188013 -20.544248 -22.822808 -25.679854 -22.999092 -20.540434 -17.964916 -15.398857 -12.990375 -10.402209 -7.888263 -5.504909 -5.217892 -5.109841 -5.014187 -4.908558 -4.811807 -4.704282 -4.605555 -4.504613 -4.406546 -4.292540 -4.204043 -4.088770 -3.995524 -3.905669 -3.796544 -3.707958 -3.596449 -3.490966 -3.382869 -3.293054 -3.185821 -3.088417 -2.971214 -2.880314 -2.772518 -2.677986 -2.569794 -2.473668 -2.365096 -2.276422 -2.179232 -2.068195 -1.973110 -1.859565 -1.771873 -1.669422 -1.569953 -1.462626 -1.364911 -1.258100 -1.159318 -1.050486 -0.959979 -0.849149 -0.749421 -0.640950 -0.547122 -0.451754 -0.344463 -0.252269 -0.134625 -0.051640 0.052970 0.154112 0.266505 0.353926 0.468739 0.561666 0.673810 0.759169 0.881697 0.973207 1.082409 1.170424 1.282163 1.378096 1.472728 1.586454 1.678473 1.785688 1.873862 1.984090 2.086021 2.196799 2.292400 2.386097 2.493190 2.601726 2.694346 2.803450 2.901878 3.011959 3.103050 3.196979 3.294507 3.397563 3.504076 3.600163 3.712539 3.809573 3.919799 4.012314 4.120694 4.216406 4.322895 4.416466 4.522871 4.623917 4.735925 4.826929 7.361253 9.647208 12.337984 14.870260 17.439730 19.921717 22.524080 25.125903/;
等同于
my @xs = ('22.595451', '20.089094', '17.380813', '15.091260', 'etc...');
但是，如您所见，可以节省 一堆 的输入。
所以现在你有了一堆字符串，你可以将它们用作数字，perl 会自动为你进行转换（通常推荐），或者如果它们的字符串性冒犯了你，你可以明确地做一个过早的手动转换。
当你想转换数组或列表时，考虑map或foreach。
@ys = map { 1 * $_ } @ys;
或
foreach my $element (@ys) {
$element *= 1; # or += 0 both work.
}
...但说真的，这到底给你带来了什么？如果您允许 Perl 在闲暇时进行转换，那么这些值将变成双重值，并且如果您将它们用作字符串则不需要重新转换。使用手动转换，您冒着最终可能需要重新字符串化的纯数字值的风险，因此可能会出现舍入错误苹果的第二次咬合。
只有当您需要转换为 BigInt、BigFloat 或类似对象（也就是说，您担心自动转换为浮点数可能会导致精度损失）；或者，如果您准备通过 JSON 或 YAML 输出值到关心 'text representation of a number' (49) 和 'quoted strings of digits' ("49" 之间差异的系统)，但请注意，这算作重新字符串化。
我不明白 qw 在 Perl 中的作用，这是我在调试此 qw/string/.
我试图了解以下代码中出了什么问题我正在对数据进行简单操作（乘以一 (1.0)）。
原始代码是真实案例中情况的简化版本
use v5.16;
use Math::Geometry::Planar qw(SegmentLineIntersection);
sub x_intercepts {
my ($points) = @_;
die 'Must pass at least 2 points' unless @$points >= 2;
my @intercepts;
my @x_axis = ( [0, 2000], [1, 2000] );
foreach my $i (0 .. $#$points - 1) {
my $intersect = SegmentLineIntersection([@$points[$i,$i+1], @x_axis]);
push @intercepts, $intersect if $intersect;
}
return \@intercepts;
}
my @xs = qw/22.595451 20.089094 17.380813 15.091260 12.477935 10.054821 7.270003 4.804673 4.728526 4.619254 4.526920 4.418416 4.321419 4.219890 4.123336 4.009777 3.912648 3.804183 3.705847 3.597756 3.512301 3.393413 3.301963 3.196725 3.098560 3.007482 2.899825 2.801002 2.688680 2.598862 2.496139 2.393526 2.282183 2.190449 2.084530 1.987778 1.877562 1.788788 1.678473 1.578123 1.467071 1.373372 1.283629 1.176670 1.071805 0.975422 0.877622 0.767820 0.667409 0.562480 0.469068 0.354589 0.264291 0.152522 0.063765 -0.045323 -0.136783 -0.248559 -0.343694 -0.459178 -0.551917 -0.640803 -0.755502 -0.845535 -0.955227 -1.045879 -1.155600 -1.254556 -1.365163 -1.461669 -1.571370 -1.658043 -1.772672 -1.865942 -1.981037 -2.073702 -2.176205 -2.276184 -2.367371 -2.476278 -2.567385 -2.686326 -2.777433 -2.884357 -2.980067 -3.087754 -3.183607 -3.291003 -3.386942 -3.495822 -3.586759 -3.702955 -3.793550 -3.900680 -3.999672 -4.093094 -4.200047 -4.301026 -4.399742 -4.493190 -4.602013 -4.705124 -4.812383 -4.907510 -5.022904 -5.109829 -5.214304 -5.317662 -7.703172 -10.350131 -12.921361 -15.431203 -18.188013 -20.544248 -22.822808 -25.679854 -22.999092 -20.540434 -17.964916 -15.398857 -12.990375 -10.402209 -7.888263 -5.504909 -5.217892 -5.109841 -5.014187 -4.908558 -4.811807 -4.704282 -4.605555 -4.504613 -4.406546 -4.292540 -4.204043 -4.088770 -3.995524 -3.905669 -3.796544 -3.707958 -3.596449 -3.490966 -3.382869 -3.293054 -3.185821 -3.088417 -2.971214 -2.880314 -2.772518 -2.677986 -2.569794 -2.473668 -2.365096 -2.276422 -2.179232 -2.068195 -1.973110 -1.859565 -1.771873 -1.669422 -1.569953 -1.462626 -1.364911 -1.258100 -1.159318 -1.050486 -0.959979 -0.849149 -0.749421 -0.640950 -0.547122 -0.451754 -0.344463 -0.252269 -0.134625 -0.051640 0.052970 0.154112 0.266505 0.353926 0.468739 0.561666 0.673810 0.759169 0.881697 0.973207 1.082409 1.170424 1.282163 1.378096 1.472728 1.586454 1.678473 1.785688 1.873862 1.984090 2.086021 2.196799 2.292400 2.386097 2.493190 2.601726 2.694346 2.803450 2.901878 3.011959 3.103050 3.196979 3.294507 3.397563 3.504076 3.600163 3.712539 3.809573 3.919799 4.012314 4.120694 4.216406 4.322895 4.416466 4.522871 4.623917 4.735925 4.826929 7.361253 9.647208 12.337984 14.870260 17.439730 19.921717 22.524080 25.125903/;
# -1 1.0 3 4 5 6 7 7 8 9 10/;
my @ys = qw/3699.316162 3676.939697 3659.950195 3641.476318 3605.965576 3580.152588 3555.092529 3528.118408 3509.595703 3504.416504 3508.355957 3510.452881 3510.304443 3499.548340 3499.943848 3493.196533 3499.488770 3494.984375 3494.390137 3493.938965 3492.606689 3493.434814 3488.926514 3488.890869 3484.599854 3488.077393 3484.177979 3477.801758 3478.098877 3472.040039 3477.642090 3477.802002 3472.908447 3478.532715 3469.805420 3472.759766 3464.269043 3463.950684 3465.888184 3458.441650 3459.006104 3455.686035 3455.677490 3454.548828 3454.241211 3455.250000 3449.803711 3447.423340 3457.498779 3448.445557 3453.106689 3447.701172 3444.543945 3448.558350 3450.073730 3449.884033 3444.751953 3444.056152 3444.825195 3449.671143 2593.656494 788.985779 776.407776 776.385925 767.522522 774.794250 770.596008 775.218384 770.962769 766.214294 766.735962 759.847351 760.073486 760.026489 753.721741 755.601929 753.942566 758.356506 747.932617 746.332214 746.464844 747.055115 750.173706 737.463379 739.810486 742.011475 744.332581 743.022461 737.302490 737.396606 734.325256 737.305359 740.642395 734.709717 735.754089 737.961182 740.697510 727.310913 730.918640 728.325012 721.845459 728.389893 727.765625 729.961243 725.608459 723.581909 730.736084 720.707764 720.398193 691.499390 657.534546 628.854431 615.219727 572.711365 561.505127 539.865173 517.139709 545.076416 580.880005 602.851135 628.006104 657.119263 683.746033 692.044373 716.640320 715.451294 715.415405 718.968018 723.698669 729.758606 728.564514 734.523376 731.454468 736.899780 731.257263 729.390686 732.837463 730.479431 733.497803 735.362732 742.581543 742.998108 735.918579 738.190002 738.108337 738.154297 740.425537 739.496033 743.105835 737.412537 740.537354 747.498108 747.424194 748.992920 752.244263 755.603455 756.611755 761.916504 762.920715 752.261658 758.293823 755.664062 753.728882 756.746338 754.825684 755.080444 761.192383 761.955505 763.209351 760.402771 764.342224 775.400940 767.148621 775.184998 777.084595 778.357117 776.217163 1086.248291 3444.476807 3438.105957 3440.625000 3438.325195 3438.430420 3449.251709 3453.216309 3452.126465 3458.547119 3451.694336 3456.417725 3457.336426 3457.777832 3455.553955 3457.256348 3458.823486 3459.088623 3459.492187 3463.538818 3466.455078 3456.521240 3459.809082 3457.505127 3462.721191 3466.518066 3467.562744 3469.211182 3469.120361 3464.043945 3466.291992 3472.698486 3476.146729 3471.635254 3472.539551 3475.163574 3473.687744 3479.102051 3488.351807 3482.367432 3481.961914 3484.844238 3481.511719 3482.469238 3488.947021 3488.882080 3491.247314 3499.116699 3511.889893 3539.602783 3565.981445 3598.203613 3628.028076 3657.928955 3685.231689/;
# my @ys = 1.0 * @ys;
my @input_list ;
foreach my $i ( 0..$#ys ) {
push @input_list, [ $xs[$i], $ys[$i] ] ;
}
my $intercept_list = x_intercepts(\@input_list) ;
say join ",", @$_ for @$intercept_list ;
我只是通过注释掉
来激活这一行# my @ys = 1.0 * @ys;
Must pass at least 2 points at test2.pl line 7.
这表明 1.0 * qw_stuff 正在做一些超出我预期的事情。
我运行
my @ys = 1 * scalar(@ys); my @ys = qw/@ys/;
但同样的错误仍然存在。
如何在 Perl 中对整数和 qw 之间的数据进行简单的操作？
引用词：
my @xs = qw/22.595451 20.089094 17.380813 15.091260 12.477935 10.054821 7.270003 4.804673 4.728526 4.619254 4.526920 4.418416 4.321419 4.219890 4.123336 4.009777 3.912648 3.804183 3.705847 3.597756 3.512301 3.393413 3.301963 3.196725 3.098560 3.007482 2.899825 2.801002 2.688680 2.598862 2.496139 2.393526 2.282183 2.190449 2.084530 1.987778 1.877562 1.788788 1.678473 1.578123 1.467071 1.373372 1.283629 1.176670 1.071805 0.975422 0.877622 0.767820 0.667409 0.562480 0.469068 0.354589 0.264291 0.152522 0.063765 -0.045323 -0.136783 -0.248559 -0.343694 -0.459178 -0.551917 -0.640803 -0.755502 -0.845535 -0.955227 -1.045879 -1.155600 -1.254556 -1.365163 -1.461669 -1.571370 -1.658043 -1.772672 -1.865942 -1.981037 -2.073702 -2.176205 -2.276184 -2.367371 -2.476278 -2.567385 -2.686326 -2.777433 -2.884357 -2.980067 -3.087754 -3.183607 -3.291003 -3.386942 -3.495822 -3.586759 -3.702955 -3.793550 -3.900680 -3.999672 -4.093094 -4.200047 -4.301026 -4.399742 -4.493190 -4.602013 -4.705124 -4.812383 -4.907510 -5.022904 -5.109829 -5.214304 -5.317662 -7.703172 -10.350131 -12.921361 -15.431203 -18.188013 -20.544248 -22.822808 -25.679854 -22.999092 -20.540434 -17.964916 -15.398857 -12.990375 -10.402209 -7.888263 -5.504909 -5.217892 -5.109841 -5.014187 -4.908558 -4.811807 -4.704282 -4.605555 -4.504613 -4.406546 -4.292540 -4.204043 -4.088770 -3.995524 -3.905669 -3.796544 -3.707958 -3.596449 -3.490966 -3.382869 -3.293054 -3.185821 -3.088417 -2.971214 -2.880314 -2.772518 -2.677986 -2.569794 -2.473668 -2.365096 -2.276422 -2.179232 -2.068195 -1.973110 -1.859565 -1.771873 -1.669422 -1.569953 -1.462626 -1.364911 -1.258100 -1.159318 -1.050486 -0.959979 -0.849149 -0.749421 -0.640950 -0.547122 -0.451754 -0.344463 -0.252269 -0.134625 -0.051640 0.052970 0.154112 0.266505 0.353926 0.468739 0.561666 0.673810 0.759169 0.881697 0.973207 1.082409 1.170424 1.282163 1.378096 1.472728 1.586454 1.678473 1.785688 1.873862 1.984090 2.086021 2.196799 2.292400 2.386097 2.493190 2.601726 2.694346 2.803450 2.901878 3.011959 3.103050 3.196979 3.294507 3.397563 3.504076 3.600163 3.712539 3.809573 3.919799 4.012314 4.120694 4.216406 4.322895 4.416466 4.522871 4.623917 4.735925 4.826929 7.361253 9.647208 12.337984 14.870260 17.439730 19.921717 22.524080 25.125903/;
等同于
my @xs = ('22.595451', '20.089094', '17.380813', '15.091260', 'etc...');
但是，如您所见，可以节省 一堆 的输入。
所以现在你有了一堆字符串，你可以将它们用作数字，perl 会自动为你进行转换（通常推荐），或者如果它们的字符串性冒犯了你，你可以明确地做一个过早的手动转换。
当你想转换数组或列表时，考虑map或foreach。
@ys = map { 1 * $_ } @ys;
或
foreach my $element (@ys) {
$element *= 1; # or += 0 both work.
}
...但说真的，这到底给你带来了什么？如果您允许 Perl 在闲暇时进行转换，那么这些值将变成双重值，并且如果您将它们用作字符串则不需要重新转换。使用手动转换，您冒着最终可能需要重新字符串化的纯数字值的风险，因此可能会出现舍入错误苹果的第二次咬合。
只有当您需要转换为 BigInt、BigFloat 或类似对象（也就是说，您担心自动转换为浮点数可能会导致精度损失）；或者，如果您准备通过 JSON 或 YAML 输出值到关心 'text representation of a number' (49) 和 'quoted strings of digits' ("49" 之间差异的系统)，但请注意，这算作重新字符串化。