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<p>The key is understanding that a single index always reduces dimensionality, whereas a multiple index never does. The dimensions with multiple indexes (and unindexed dimensions) determine the indexed expression’s type. In the example above, because <code>v</code> is an array of vectors, <code>v[2, idxs]</code> reduces the array dimension but doesn’t reduce the vector dimension, so the result is a vector. In contrast, <code>v[idxs, 2]</code> does not reduce the array dimension, but does red