Problem 2159. A SUBSREF variant that accepts the 'end'-operator.

Created by J-G van der Toorn

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{"relationships":[{"relationshipType":"http://schemas.mathworks.com/matlab/code/2013/relationships/document","targetMode":"","relationshipId":"rId1","target":"/matlab/document.xml"},{"relationshipType":"http://schemas.mathworks.com/matlab/code/2013/relationships/output","targetMode":"","relationshipId":"rId2","target":"/matlab/output.xml"}],"parts":[{"partUri":"/matlab/document.xml","relationship":[],"contentType":"application/vnd.mathworks.matlab.code.document+xml","content":"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<w:document xmlns:w=\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\"><w:body><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Unfortunately, Matlab's</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>subsref</w:t></w:r><w:r><w:t> function does not support the</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>end</w:t></w:r><w:r><w:t> -operator. The</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>end</w:t></w:r><w:r><w:t> -operator is a powerfull method to refer to the rear-end of an array,</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[ a = 1:10;\n a(end-1) % is 9\n a(end-2:end) % is [8 9 10]]]></w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>It works similar for cell arrays and struct-arrays.</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Alhough</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>subsref</w:t></w:r><w:r><w:t> is quite powerful, and accepts for example the</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>:</w:t></w:r><w:r><w:t> colon oparator, it fails to process more complex stings, including</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>end</w:t></w:r><w:r><w:t> -operators.</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>This assignment is to create a function that accepts those more complex element definitions.</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>For example</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[ s.a.b(3).c{2}.d = 'a':'z';\n subsref(s,substruct('.','a','.','b','()',{3},'.','c','{}',{2},'.','d','()',{1:3}))]]></w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>returns</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[ ans = \n\n abc]]></w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>And</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[subsrefbetter(s,substruct('.','a','.','b','()',{3},'.','c','{}',{2},'.','d','()',{'[1 end]'}))]]></w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>should return</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[ ans = \n\n az]]></w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>and</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[subsrefbetter(s,substruct('.','a','.','b','()',{3},'.','c','{}',{2},'.','d','()',{'end-2:end'}))]]></w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>should return</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"code\"/></w:pPr><w:r><w:t><![CDATA[ ans =\n\n xyz]]></w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>The function</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>subsrefbetter</w:t></w:r><w:r><w:t> should accept both structures like created with</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>substruct</w:t></w:r><w:r><w:t>, and list of arguments like accepted by</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:rFonts w:cs=\"monospace\"/></w:rPr><w:t>substruct</w:t></w:r><w:r><w:t>.</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>That's all.</w:t></w:r></w:p></w:body></w:document>"},{"partUri":"/matlab/output.xml","contentType":"text/xml","content":"<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\" ?><embeddedOutputs><metaData><evaluationState>manual</evaluationState><layoutState>code</layoutState><outputStatus>ready</outputStatus></metaData><outputArray type=\"array\"/><regionArray type=\"array\"/></embeddedOutputs>"}]}

Unfortunately, Matlab's <tt>subsref</tt> function does not support the <tt>end</tt> -operator. The <tt>end</tt> -operator is a powerfull method to refer to the rear-end of an array,<pre> a = 1:10;
 a(end-1) % is 9
 a(end-2:end) % is [8 9 10]</pre>It works similar for cell arrays and struct-arrays.Alhough <tt>subsref</tt> is quite powerful, and accepts for example the <tt>:</tt> colon oparator, it fails to process more complex stings, including <tt>end</tt> -operators.This assignment is to create a function that accepts those more complex element definitions.For example<pre> s.a.b(3).c{2}.d = 'a':'z';
 subsref(s,substruct('.','a','.','b','()',{3},'.','c','{}',{2},'.','d','()',{1:3})) </pre>returns<pre> ans = </pre><pre> abc </pre>And<pre class="language-matlab">subsrefbetter(s,substruct('.','a','.','b','()',{3},'.','c','{}',{2},'.','d','()',{'[1 end]'})) 
</pre>should return<pre> ans = </pre><pre> az </pre>and<pre class="language-matlab">subsrefbetter(s,substruct('.','a','.','b','()',{3},'.','c','{}',{2},'.','d','()',{'end-2:end'})) 
</pre>should return<pre> ans =</pre><pre> xyz</pre>The function <tt>subsrefbetter</tt> should accept both structures like created with <tt>substruct</tt>, and list of arguments like accepted by <tt>substruct</tt>.That's all.

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Last Solution submitted on Dec 03, 2018

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Andrew Newell on 20 May 2017

Pity that eval is forbidden - I had quite an elegant solution using it.

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colon data structure end indexing subsref very useful

Problem 2159. A SUBSREF variant that accepts the 'end'-operator.

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Problem 2159. A SUBSREF variant that accepts the 'end'-operator.

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