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    copied!<p>This works for me using indexing in python.</p> <pre><code> &gt;&gt;&gt;from ROOT import * &gt;&gt;&gt;vec1 = std.vector('double')() &gt;&gt;&gt;vec2 = std.vector('double')() &gt;&gt;&gt;vec_vec = std.vector(std.vector('double'))() &gt;&gt;&gt;for i in range(3): &gt;&gt;&gt; vec1.push_back(i) &gt;&gt;&gt;for i in range(5): &gt;&gt;&gt; vec2.push_back(i) &gt;&gt;&gt;vec_vec.push_back(vec1) &gt;&gt;&gt;vec_vec.push_back(vec2) &gt;&gt;&gt;len(vec_vec) 2 &gt;&gt;&gt;len(vec_vec[0]) 3 &gt;&gt;&gt;len(vec_vec[1]) 5 &gt;&gt;&gt;vec_vec[1][2] 2.0 </code></pre> <p>In your example the error says:</p> <pre><code> TypeError: 'vector&lt;vector&lt;float&gt; &gt;' object is unindexable </code></pre> <p>After calling the constructor std.vector(type)() you have different types that indicate that an allocator for memory space is working.</p> <pre><code> &gt;&gt;&gt;type(vec1) &lt;class 'ROOT.vector&lt;double,allocator&lt;double&gt; &gt;'&gt; &gt;&gt;&gt;type(vec_vec) &lt;class 'ROOT.vector&lt;vector&lt;double,allocator&lt;double&gt; &gt;,allocator&lt;vector&lt;double,allocator&lt;double&gt; &gt; &gt; &gt;'&gt; </code></pre> <p>To import such vectors from a TTree use setBranchAddress like in this example:</p> <pre><code> &gt;&gt;&gt;tree = file.Get('tree') &gt;&gt;&gt;tree.SetBranchAddress("nested",vec_vec) &gt;&gt;&gt;N = tree.GetEntries() &gt;&gt;&gt;for i in range(N): &gt;&gt;&gt; vec_vec.clear() &gt;&gt;&gt; tree.GetEntry(i) &gt;&gt;&gt; print vec_vec[0][0] </code></pre> <p>Also note that this may be significantly faster after using</p> <pre><code> &gt;&gt;&gt;tree.setBranchStatus('*',0) &gt;&gt;&gt;tree.setBranchStatus('nested',1) </code></pre>
 

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