mosesdecoder/scripts/analysis/sentence-by-sentence.pl
Jeroen Vermeulen ef028446f3 Add license notices to scripts.
This is not pleasant to read (and much, much less pleasant to write!) but
sort of necessary in an open project.  Right now it's quite hard to figure
out what is licensed how, which doesn't matter much to most people but can
suddenly become very important when people want to know what they're being
allowed to do.

I kept the notices as short as I could.  As far as I could see, everything
without a clear license notice is LGPL v2.1 or later.
2015-05-29 18:30:26 +07:00

548 lines
21 KiB
Perl
Executable File

#!/usr/bin/env perl
#
# This file is part of moses. Its use is licensed under the GNU Lesser General
# Public License version 2.1 or, at your option, any later version.
# $Id$
#sentence-by-sentence: take in a system output, with any number of factors, and a reference translation, also maybe with factors, and show each sentence and its errors
#usage: sentence-by-sentence SYSOUT [REFERENCE]+ > sentences.html
use warnings;
use strict;
use Getopt::Long;
my $sourcefile = undef;
my @truthfiles;
GetOptions(
"source|s=s" => \$sourcefile,
"reference|r=s" => \@truthfiles
) or exit(1);
my @sysoutfiles = @ARGV;
if (scalar(@sysoutfiles) == 0 || scalar(@truthfiles) == 0)
{
print STDERR "usage: $0 system_output(s) > sentence-by-sentence.html
Options:
--source,-s STRING foreign input (can be used multiple times)
--reference,-r STRING English truth (can be used multiple times)
N-grams are colored by the number of supporting references:
red for fewest, green for most, mediate shades otherwise.\n";
exit(1);
}
####################################################################################################################
my @TRUTHS = () x scalar(@truthfiles);
for(my $i = 0; $i < scalar(@truthfiles); $i++)
{
open($TRUTHS[$i], "<$truthfiles[$i]") or die "couldn't open '$truthfiles[$i]' for read: $!\n";
binmode($TRUTHS[$i], ":utf8");
}
my @SYSOUTS = () x scalar(@sysoutfiles);
for(my $i = 0; $i < scalar(@sysoutfiles); $i++)
{
open($SYSOUTS[$i], "<$sysoutfiles[$i]") or die "couldn't open '$sysoutfiles[$i]' for read: $!\n";
binmode($SYSOUTS[$i], ":utf8");
}
binmode(STDOUT, ":utf8");
if (defined $sourcefile)
{
open(SOURCE, "<$sourcefile") or die "couldn't open '$sourcefile' for read: $!\n";
binmode(SOURCE, ":utf8");
}
my @bleuScores;
for(my $i = 0; $i < scalar(@sysoutfiles); $i++) {push @bleuScores, [];}
my @htmlSentences;
my @javascripts;
my @htmlColors = ('#99ff99', '#aaaaff', '#ffff99', '#ff9933', '#ff9999'); #color sentences by rank (split in n tiers)
my $ngramSingleRefColor = '#aaffaa';
my @ngramMultirefColors = ('#ff9999', '#ff9933', '#ffff99', '#a0a0ff', '#99ff99'); #arbitrary-length list; first entry is used for worst n-grams
my $numSentences = 0;
my (@sLines, @eLines);
while(readLines(\@SYSOUTS, \@sLines) && readLines(\@TRUTHS, \@eLines))
{
#create array of lines of HTML
my @html = ("<div class=\"sentence_%%%%\" id=\"sentence$numSentences\">"); #%%%% is a flag to be replaced
my (@sFactors, @eFactors, $sourceFactors);
#process source
if (defined $sourcefile)
{
my $sourceLine = <SOURCE>;
escapeMetachars($sourceLine); #remove inconsistencies in encoding
$sourceFactors = extractFactorArrays($sourceLine);
push @html, "<tr><td class=\"sent_title\">Source</td><td class=\"source_sentence\" id=\"source$numSentences\">"
. getFactoredSentenceHTML($sourceFactors) . "</td></tr>\n";
}
#process truth
for(my $j = 0; $j < scalar(@truthfiles); $j++)
{
escapeMetachars($eLines[$j]); #remove inconsistencies in encoding
push @eFactors, extractFactorArrays($eLines[$j]);
push @html, "<tr><td class=\"sent_title\">Ref $j</td><td class=\"truth_sentence\" id=\"truth${numSentences}_$j\">"
. getFactoredSentenceHTML($eFactors[$j]) . "</td></tr>\n";
}
#process sysouts
my @bleuData;
for(my $j = 0; $j < scalar(@sysoutfiles); $j++)
{
escapeMetachars($sLines[$j]); #remove inconsistencies in encoding
push @sFactors, extractFactorArrays($sLines[$j]);
push @bleuData, getBLEUSentenceDetails($sFactors[$j], \@eFactors, 0);
push @{$bleuScores[$j]}, [$numSentences, $bleuData[$j]->[0], 0]; #the last number will be the rank
my $pwerData = getPWERSentenceDetails($sFactors[$j], \@eFactors, 0);
push @html, "<tr><td class=\"sent_title\">Output $j</td><td class=\"sysout_sentence\" id=\"sysout$numSentences\">"
. getFactoredSentenceHTML($sFactors[$j], $pwerData) . "</td></tr>\n";
push @html, "<tr><td class=\"sent_title\">N-grams</td><td class=\"sysout_ngrams\" id=\"ngrams$numSentences\">"
. getAllNgramsHTML($sFactors[$j], $bleuData[$j]->[1], scalar(@truthfiles)) . "</td></tr>\n";
}
splice(@html, 1, 0, "<div class=\"bleu_report\"><b>Sentence $numSentences)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;BLEU:</b> "
. join("; ", map {sprintf("%.4lg", $_->[0]->[0]) . " (" . join('/', map {sprintf("%.4lg", $_)} @{$_->[0]}[1 .. 4]) . ") "} @bleuData) . "</div><table>\n");
push @html, "</table></div>\n";
push @htmlSentences, join('', @html);
$numSentences++;
@sLines = (); @eLines = (); #clear writable arrays to be refilled
}
foreach my $sysoutfh (@SYSOUTS) {close($sysoutfh);}
foreach my $truthfh (@TRUTHS) {close($truthfh);}
my $stylesheet = "<style type=\"text/css\">
.legend {background: #fff; border: 1px solid #000; padding: 2px; margin-bottom: 10px; margin-right: 15px}
.legend_title {font-weight: bold; font-size: medium; text-decoration: underline}
div.bleu_report {margin-bottom: 5px}
td.sent_title {font-weight: bold; font-size: medium; margin-bottom: 12px}
.source_sentence {background: #ffcccc; border: 1px solid #bbb}
.truth_sentence {background: #ccffcc; border: 1px solid #bbb}
.sysout_sentence {background: #ccccff; border: 1px solid #bbb}
table.sentence_table {border: none}
.sysout_ngrams {background: #fff; border: 1px solid #bbb}
table.ngram_table {}
td.ngram_cell {padding: 1px}\n";
for(my $i = 0; $i < scalar(@htmlColors); $i++)
{
$stylesheet .= ".sentence_tier$i {background: $htmlColors[$i]; border: 1px solid #000088; padding: 0px 8px 0px 8px} //entire composition for a given sentence\n";
$stylesheet .= "div.sentence_tier$i td {margin: 8px 0px 8px 0px}\n";
}
$stylesheet .= "</style>\n";
print "<html><head><meta http-equiv=\"Content-type\" content=\"text/html; charset=UTF-8\">\n";
print "<title>[" . join(', ', @sysoutfiles) . "] vs. [" . join(', ', @truthfiles) . "]: Sentence-by-Sentence Comparison</title>$stylesheet</head><body>\n";
foreach my $systemScores (@bleuScores) {rankSentencesByBLEU($systemScores);}
#javascript to sort by BLEU for any system, by order in corpus ...
print "<script type=\"text/javascript\">
var selectedSysout = 0; //index of system currently being used to rank/sort
function selectSysout(index)
{
//update the BLEU-range text shown in the legend
var legend = document.getElementById('legendBLEU');
var rows = legend.getElementsByTagName('tr');
for(var i = 0; i < rows.length; i++)
{
var cell = rows[i].childNodes[1];
var spans = cell.getElementsByTagName('span');
cell.childNodes[0].nodeValue = spans[index].firstChild.nodeValue; //something like '0.1 - 0.3'
}
//update the background colors of the sentence divs
var allSentences = document.getElementById('all_sentences');
var sentences = allSentences.childNodes;
for(var i = 0; i < sentences.length; i++)
{
if(typeof sentences[i].tagName != 'undefined' && sentences[i].tagName.toLowerCase() == 'div') //text nodes have undefined tagName
{
var tierSpans = sentences[i].firstChild.childNodes;
sentences[i].childNodes[2].className = tierSpans[index].firstChild.nodeValue; //something like 'tier3'
}
}
selectedSysout = index; //selectedSysout is a flag to the sort functions
}
function sortByBLEU()
{
var body = document.getElementById('all_sentences'); var row;
switch(selectedSysout)
{\n";
for(my $i = 0; $i < scalar(@sysoutfiles); $i++)
{
print "case $i:
{";
my %rank2index = map {$bleuScores[$i]->[$_]->[2] => $_} (0 .. scalar(@htmlSentences) - 1);
foreach my $rank (sort {$a <=> $b} keys %rank2index)
{
print "\trow = document.getElementById('everything" . $rank2index{$rank} . "');\n";
print "\tbody.removeChild(row); body.appendChild(row);\n";
}
print "break;}\n";
}
print "}
}
function sortByCorpusOrder()
{
var body = document.getElementById('all_sentences'); var row;\n";
for(my $j = 0; $j < scalar(@htmlSentences); $j++)
{
print "\trow = document.getElementById('everything$j');\n";
print "\tbody.removeChild(row); body.appendChild(row);\n";
}
print "}
</script>\n";
#legends for background colors of sentences and n-grams
my (@minBLEU, @maxBLEU);
my @bleuTiers = () x scalar(@htmlSentences); #for each sentence, arrayref of tier indices for each system
for(my $i = 0; $i < scalar(@sysoutfiles); $i++)
{
my @a = (1e9) x scalar(@htmlColors);
my @b = (-1e9) x scalar(@htmlColors);
for(my $k = 0; $k < scalar(@htmlSentences); $k++)
{
my $tier = int($bleuScores[$i]->[$k]->[2] / (scalar(@htmlSentences) / scalar(@htmlColors)));
push @{$bleuTiers[$k]}, $tier;
if($bleuScores[$i]->[$k]->[1]->[0] < $a[$tier]) {$a[$tier] = $bleuScores[$i]->[$k]->[1]->[0];}
if($bleuScores[$i]->[$k]->[1]->[0] > $b[$tier]) {$b[$tier] = $bleuScores[$i]->[$k]->[1]->[0];}
}
push @minBLEU, \@a;
push @maxBLEU, \@b;
}
print "<table border=0><tr><td><div id=\"legendBLEU\" class=\"legend\"><span class=\"legend_title\">Sentence Background Colors => BLEU Ranges</span><table border=0>";
for(my $k = 0; $k < scalar(@htmlColors); $k++)
{
print "<tr><td style=\"width: 15px; height: 15px; background: " . $htmlColors[$k] . "\"></td><td align=left style=\"padding-left: 12px\">"
. sprintf("%.4lg", $minBLEU[0]->[$k]) . " - " . sprintf("%.4lg", $maxBLEU[0]->[$k]);
for(my $j = 0; $j < scalar(@sysoutfiles); $j++)
{
print "<span style=\"display: none\">" . sprintf("%.4lg", $minBLEU[$j]->[$k]) . " - " . sprintf("%.4lg", $maxBLEU[$j]->[$k]) . "</span>";
}
print "</td></tr>";
}
print "</table></div></td>\n";
print "<td><div class=\"legend\"><span class=\"legend_title\">N-gram Colors => Number of Matching Reference Translations</span><table border=0>";
for(my $k = 1; $k <= scalar(@truthfiles); $k++)
{
print "<tr><td style=\"width: 15px; height: 15px; background: " . getNgramColorHTML($k, scalar(@truthfiles)) . "\"></td><td align=left style=\"padding-left: 12px\">$k</td></tr>";
}
print "</table></div></td></tr></table><div style=\"font-weight: bold; margin-bottom: 15px\">
PWER errors are marked in red on output sentence displays.</div>
<div style=\"margin-bottom: 8px\">Color by system # "
. join(' | ', map {"<a href=\"javascript:selectSysout($_);\">$_</a>" . (($_ == '0') ? " (default)" : "")} (0 .. scalar(@sysoutfiles) - 1)) . "</div>
<div style=\"margin-bottom: 8px\">Sort by <a href=\"javascript:sortByBLEU();\">BLEU score</a> | <a href=\"javascript:sortByCorpusOrder();\">corpus order</a> (default)</div>\n";
#sentence boxes
print "<div id=\"all_sentences\">";
for(my $j = 0; $j < scalar(@htmlSentences); $j++)
{
print "<div id=\"everything$j\" style=\"margin: 0px; padding: 0px\">";
print "<div class=\"ranks_container\" style=\"display: none\">" . join('', map {"<span>sentence_tier$_</span>"} @{$bleuTiers[$j]}) . "</div>";
print "<hr width=98%>";
# my $bgcolor = getSentenceBGColorHTML($bleuScores[0]->[$j], $i); #i is now # of sentences
my $tierNum = $bleuTiers[$j]->[0];
$htmlSentences[$j] =~ s/%%%%/tier$tierNum/;
print "$htmlSentences[$j]</div>\n";
}
print "</div></body></html>";
##################### utils #####################
#arguments: a, b (scalars)
sub min
{
my ($a, $b) = @_;
return ($a < $b) ? $a : $b;
}
#arguments: a, b (scalars)
sub max
{
my ($a, $b) = @_;
return ($a > $b) ? $a : $b;
}
#arguments: a list of elements
#return undef for an empty list, the max element otherwise
sub maxN
{
if(scalar @_ == 0) {return undef;}
my $val = shift @_;
foreach my $e (@_) {if($e > $val) {$val = $e;}}
return $val;
}
#arguments: x
sub my_log
{
return -9999999999 unless $_[0];
return log($_[0]);
}
#arguments: x
sub round
{
my $x = shift;
return ($x - int($x) < .5) ? int($x) : int($x) + 1;
}
#escape HTML metacharacters for display purposes and to allow for consistent string comparison
#arguments: string to be formatted in place
#return: none
sub escapeMetachars
{
my $str = shift;
$str =~ s/&\s+/&amp; /;
$str =~ s/<\s+/&lt; /;
$str =~ s/>\s+/&gt; /;
}
###############################################################################################################################################################
#read one line from each of any number of filehandles
#arguments: arrayref of filehandles, (empty) arrayref to be filled with read lines
#return: 1 on success, 0 on failure (on failure the lines arrayref's value isn't defined)
sub readLines
{
my ($refFilehandles, $refLines) = @_;
foreach my $fh (@$refFilehandles)
{
my $line = <$fh>;
return 0 unless defined($line);
push @$refLines, $line;
}
return 1;
}
#arguments: line read from corpus file
#return: sentence (arrayref of arrayrefs of factor strings) taken from line
sub extractFactorArrays
{
my $line = shift;
die "" if !defined $line;
chomp $line;
$line =~ s/^\s*|\s*$//g; #added by Ondrej to handle moses-mert-parallel output
my @words = split(/\s+/, $line);
my @factors = map {my @f = split(/\|/, $_); \@f;} @words;
return \@factors;
}
#can handle multiple reference translations; assume at least one
#arguments: sysout sentence (arrayref of arrayrefs of factor strings), truth sentences (arrayref of same), factor index to use
#return: arrayref of [arrayref of [overall BLEU score, n-gram precisions], arrayref of matching n-gram [start index, length, arrayref of indices of matching references]]
sub getBLEUSentenceDetails
{
my $maxNgramOrder = 4;
my ($refSysOutput, $refTruths, $factorIndex) = @_;
my $length_translation = scalar(@$refSysOutput); #length of sysout sentence
my @length_references = map {scalar(@$_)} @$refTruths;
my $closestTruthLength = (sort(map {abs($_ - $length_translation)} @length_references))[0];
my @correct = (0) x $maxNgramOrder; #n-gram counts
my @total = (0) x $maxNgramOrder; #n-gram counts
my $returnData = [[], []];
my %REF_GRAM; #hash from n-gram to arrayref with # of times found in each reference
my $ngramMatches = []; #arrayref of n-gram [start index, length]
for(my $j = 0; $j < scalar(@$refTruths); $j++)
{
for(my $i = 0; $i < $length_references[$j]; $i++)
{
my $gram = '';
for(my $k = 0; $k < min($i + 1, $maxNgramOrder); $k++) #run over n-gram orders
{
$gram = $refTruths->[$j]->[$i - $k]->[$factorIndex] . " " . $gram;
#increment the count for the given n-gram and given reference number
if(!exists $REF_GRAM{$gram})
{
my @tmp = (0) x scalar @$refTruths;
$tmp[$j] = 1;
$REF_GRAM{$gram} = \@tmp;
}
else
{
$REF_GRAM{$gram}->[$j]++;
}
}
}
}
for(my $i = 0; $i < $length_translation; $i++)
{
my $gram = '';
for(my $k = 0; $k < min($i + 1, $maxNgramOrder); $k++) #run over n-gram orders
{
$gram = $refSysOutput->[$i - $k]->[$factorIndex] . " " . $gram;
if(exists $REF_GRAM{$gram}) #this n-gram was found in at least one reference
{
$correct[$k]++;
my @indices = ();
my $notOvercounting = 0; #make sure we don't 'match' against truth n-grams whose instances have all been used already
for(my $m = 0; $m < scalar(@{$REF_GRAM{$gram}}); $m++)
{
if($REF_GRAM{$gram}->[$m] > 0)
{
push @indices, $m;
$REF_GRAM{$gram}->[$m]--;
$notOvercounting = 1;
}
}
if($notOvercounting == 1) {push @$ngramMatches, [$i - $k, $k + 1, \@indices];}
}
}
}
my $brevity = ($length_translation > $closestTruthLength || $length_translation == 0) ? 1 : exp(1 - $closestTruthLength / $length_translation);
my @pct;
my ($logsum, $logcount) = (0, 0);
for(my $i = 0; $i < $maxNgramOrder; $i++)
{
$total[$i] = max(1, $length_translation - $i);
push @pct, ($total[$i] == 0) ? -1 : $correct[$i] / $total[$i];
if($total[$i] > 0)
{
$logsum += my_log($pct[$i]);
$logcount++;
}
}
my $bleu = $brevity * exp($logsum / $logcount);
$returnData->[0] = [$bleu, @pct];
$returnData->[1] = $ngramMatches;
return $returnData;
}
#can handle multiple sentence translations; assume at least one
#arguments: sysout sentence (arrayref of arrayrefs of factor strings), truth sentences (arrayref of same), factor index to use
#return: hashref of sysout word index => whether word matches
sub getPWERSentenceDetails
{
my ($refSysOutput, $refTruths, $factorIndex) = @_;
my $matches = {};
my %truthWords; #hash from word to arrayref with number of times seen in each reference (but later holds only the max)
for(my $i = 0; $i < scalar(@$refTruths); $i++)
{
foreach my $eWord (@{$refTruths->[$i]})
{
my $factor = $eWord->[$factorIndex];
if(exists $truthWords{$factor}) {$truthWords{$factor}->[$i]++;}
else {my @tmp = (0) x scalar(@$refTruths); $tmp[$i] = 1; $truthWords{$factor} = \@tmp;}
}
}
%truthWords = map {$_ => maxN(@{$truthWords{$_}})} (keys %truthWords); #save only the max times each word is seen in a reference
for(my $j = 0; $j < scalar(@$refSysOutput); $j++)
{
if(exists $truthWords{$refSysOutput->[$j]->[$factorIndex]} && $truthWords{$refSysOutput->[$j]->[$factorIndex]} > 0)
{
$truthWords{$refSysOutput->[$j]->[$factorIndex]}--;
$matches->{$j} = 1;
}
else
{
$matches->{$j} = 0;
}
}
return $matches;
}
#assign ranks to sentences by BLEU score
#arguments: arrayref of arrayrefs of [sentence index, arrayref of [bleu score, n-gram precisions], rank to be assigned]
#return: none
sub rankSentencesByBLEU
{
my $bleuData = shift;
my $i = 0;
#sort first on score, then on 1-gram accuracy, then on sentence index
foreach my $sentenceData (reverse sort {my $c = $a->[1]->[0] <=> $b->[1]->[0]; if($c == 0) {my $d = $a->[1]->[1] <=> $b->[1]->[1]; if($d == 0) {$a->[0] cmp $b->[0];} else {$d;}} else {$c;}} @$bleuData) {$sentenceData->[2] = $i++;}
}
###############################################################################################################################################################
#write HTML for a sentence containing factors (display words in a row)
#arguments: sentence (arrayref of arrayrefs of factor strings), PWER results (hashref from word indices to 0/1 whether matched a truth word)
#return: HTML string
sub getFactoredSentenceHTML
{
my $sentence = shift;
my $pwer = 0; if(scalar(@_) > 0) {$pwer = shift;}
my $html = "<table class=\"sentence_table\"><tr>";
for(my $i = 0; $i < scalar(@$sentence); $i++) #loop over words
{
my $style = ''; #default
if($pwer ne '0' && $pwer->{$i} == 0) {$style = 'color: #cc0000; font-weight: bold';}
$html .= "<td align=center style=\"$style\">" . join("<br>", @{$sentence->[$i]}) . "</td>";
}
return $html . "</tr></table>";
}
#arguments: arrayref of [sentence index, arrayref of [bleu score, n-gram precisions], rank], number of sentences
#return: HTML color string
sub getSentenceBGColorHTML
{
my ($scoreData, $numSentences) = @_;
my $tier = int($scoreData->[2] / ($numSentences / scalar(@htmlColors))); #0..n-1
return $htmlColors[$tier];
}
#display all matching n-grams in the given sentence, with all 1-grams on one line, then arranged by picking, for each, the first line on which it fits,
# where a given word position can only be filled by one n-gram per line, so that all n-grams can be shown
#arguments: sentence (arrayref of arrayrefs of factor strings), arrayref of arrayrefs of matching n-gram [start, length, arrayref of matching reference indices],
# number of reference translations
#return: HTML string
sub getAllNgramsHTML
{
my ($sentence, $ngrams, $numTruths) = @_;
my $factorIndex = 0;
my @table = (); #array or arrayrefs each of which represents a line; each position has the index of the occupying n-gram, or -1 if none
my $n = 0; #n-gram index
foreach my $ngram (sort {$a->[0] <=> $b->[0]} @$ngrams)
{
#check for an open slot in an existing row
my $foundRow = 0;
my $r = 0;
foreach my $row (@table)
{
if(rowIsClear($row, $ngram) == 1)
{
@{$row}[$ngram->[0] .. ($ngram->[0] + $ngram->[1] - 1)] = ($n) x $ngram->[1];
push @$ngram, $r; #add row index
$foundRow = 1;
last;
}
$r++;
}
#add row if necessary
if($foundRow == 0)
{
my @row = (-1) x scalar(@$sentence);
@row[$ngram->[0] .. ($ngram->[0] + $ngram->[1] - 1)] = ($n) x $ngram->[1];
push @$ngram, scalar(@table); #add row index
push @table, \@row;
}
$n++;
}
my $html = "<table class=\"ngram_table\"><tr><td align=center>" . join("</td><td align=center>", map {$_->[$factorIndex]} @$sentence) . "</td></tr>";
my $numWords = scalar(@$sentence);
my ($curRow, $curCol) = (0, 0); #address in table
$html .= "<tr>";
foreach my $ngram (sort {my $c = $a->[3] <=> $b->[3]; if($c == 0) {$a->[0] <=> $b->[0]} else {$c}} @$ngrams) #sort by row, then word num
{
while($ngram->[0] > $curCol || $ngram->[3] > $curRow) {$html .= "<td></td>"; $curCol = ($curCol + 1) % $numWords; if($curCol == 0) {$html .= "</tr><tr>"; $curRow++;}}
$html .= "<td colspan=" . $ngram->[1] . " align=center class=\"ngram_cell\" style=\"background: " . getNgramColorHTML(scalar(@{$ngram->[2]}), $numTruths) . "\">" . join(' ', map {$_->[$factorIndex]} @{$sentence}[$ngram->[0] .. $ngram->[0] + $ngram->[1] - 1]) . "</td>";
$curCol = ($curCol + $ngram->[1]) % $numWords; if($curCol == 0) {$html .= "</tr><tr>"; $curRow++;}
}
$html .= "</tr>";
return $html . "</table>\n";
}
#auxiliary to getAllNgramsHTML(): check a table row for an empty piece at the right place for the given n-gram
#arguments: row (arrayref of ints), n-gram (arrayref of [start index, length])
#return: whether (0/1) row is clear
sub rowIsClear
{
my ($row, $ngram) = @_;
return (maxN(@{$row}[$ngram->[0] .. $ngram->[0] + $ngram->[1] - 1]) == -1) ? 1 : 0;
}
#auxiliary to getAllNgramsHTML()
#arguments: number of reference translations matching the n-gram, total number of references
#return: HTML color string
sub getNgramColorHTML
{
my ($matches, $total) = @_;
if($total == 1) {return $ngramSingleRefColor;}
return $ngramMultirefColors[round($matches / $total * (scalar(@ngramMultirefColors) - 1))];
}