Mike Gerwitz

Activist for User Freedom

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-rw-r--r--core/vector/fold.xml99
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+<?xml version="1.0"?>
+<!--
+ Copyright (C) 2018 R-T Specialty, LLC.
+
+ This file is part of tame-core.
+
+ tame-core is free software: you can redistribute it and/or modify it
+ under the terms of the GNU General Public License as
+ published by the Free Software Foundation, either version 3 of the
+ License, or (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program. If not, see <http://www.gnu.org/licenses/>.
+-->
+<package xmlns="http://www.lovullo.com/rater"
+ xmlns:c="http://www.lovullo.com/calc"
+ xmlns:t="http://www.lovullo.com/rater/apply-template"
+ core="true"
+ desc="Folding and Unfolding of Vectors">
+
+ <import package="../base" />
+ <import package="filter" export="true" />
+
+
+ The term ``fold'' is also referred to as ``reduce''---%
+ they are synonymous.
+ Unless otherwise specified,
+ folding occurs left-to-right.
+
+ \emph{Unfolding} is the opposite of a reduction---%
+ it \emph{generates} values from existing values.
+
+
+ <section title="Matrix Generation">
+ \ref{_unfold-vector-grouped_} generates a matrix from a vector---%
+ that is, it generates vectors within a vector---%
+ by grouping values.
+
+ The \tt{@class@} is used both as a predicate and as a determination of
+ the resulting vector's length
+ (the~number of rows in the resulting matrix).
+ If non-matching,
+ no columns will be produced for that respective row.
+
+ \tt{@src@} is the vector to be unfolded,
+ containing the raw values to be grouped.
+
+ \tt{@grouping@} \should be the same length as~\ref{@src@} and determines
+ the group~(row) in which the respective value should appear.
+
+ \ref{@generates@} names the resulting matrix and~\ref{@desc@} provides
+ its description.
+
+ <template name="_unfold-vector-grouped_"
+ desc="Unfold vector into a matrix by grouping">
+ <param name="@class@" desc="Iteration vector of desired length" />
+ <param name="@src@" desc="Source vector" />
+ <param name="@grouping@" desc="Grouping vector" />
+ <param name="@generates@" desc="Generator name (to yield)" />
+
+ <param name="@desc@" desc="Generator description">
+ <text>Unfolded vector </text>
+ <param-value name="@src@" />
+ <text> grouped by </text>
+ <param-value name="@grouping@" />
+ </param>
+
+ <param name="@lengthv@" desc="Length vector (of desired length)">
+ <param-class-to-yields name="@class@" />
+ </param>
+
+
+ <rate yields="_{@generates@}">
+ <c:sum of="@lengthv@" dim="matrix"
+ generates="@generates@" index="k"
+ desc="@desc@">
+ <c:cases>
+ <c:case label="Unfold on class vector match">
+ <c:when name="@lengthv@" index="k" />
+ <c:apply name="vfilter_lookup"
+ vector_pred="@grouping@" vector_src="@src@"
+ value="k"
+ start_index="#0" />
+ </c:case>
+
+ <c:otherwise label="Ignore on class vector non-match">
+ <c:set />
+ </c:otherwise>
+ </c:cases>
+ </c:sum>
+ </rate>
+ </template>
+ </section>
+</package>