Sorting and Rankings

Skip to main content

\(\newcommand{\N}{\mathbb{N}} \newcommand{\Z}{\mathbb{Z}} \newcommand{\Q}{\mathbb{Q}} \newcommand{\R}{\mathbb{R}} \newcommand{\dimens}{\operatorname{dim}} \DeclareMathOperator{\row}{\operatorname{row}} \DeclareMathOperator{\col}{\operatorname{col}} \newcommand{\im}{\operatorname{im}} \newcommand{\nulls}{\operatorname{null}} \newcommand{\minor}{\operatorname{minor}} \newcommand{\spans}{\operatorname{span}} \newcommand{\nullity}{\operatorname{nullity}} \newcommand{\kers}{\operatorname{ker}} \newcommand{\proj}{\operatorname{proj}} \newcommand{\diag}{\operatorname{diag}} \newcommand{\Tr}{\operatorname{Tr}} \newcommand{\rank}{\operatorname{rank}} \newcommand{\lt}{<} \newcommand{\gt}{>} \newcommand{\amp}{&} \definecolor{fillinmathshade}{gray}{0.9} \newcommand{\fillinmath}[1]{\mathchoice{\colorbox{fillinmathshade}{$\displaystyle \phantom{\,#1\,}$}}{\colorbox{fillinmathshade}{$\textstyle \phantom{\,#1\,}$}}{\colorbox{fillinmathshade}{$\scriptstyle \phantom{\,#1\,}$}}{\colorbox{fillinmathshade}{$\scriptscriptstyle\phantom{\,#1\,}$}}} \)

Section B.6 Sorting and Rankings

This section helps you read sorting commands as requests for positions and rankings.

scores = np.array([0.2, 0.9, 0.5])
doc_names = np.array(["D0", "D1", "D2"])

np.argsort(scores)        # indices from smallest score to largest
np.argsort(scores)[::-1]  # indices from largest score to smallest

ranking = doc_names[np.argsort(scores)[::-1]]

Sorting positions.

np.argsort(scores)

Read as. Indices from smallest score to largest score.

Shape/return. An index array.

Used for. Sorting.

Reverse ranking.

np.argsort(scores)[::-1]

Read as. Indices from largest score to smallest score.

Shape/return. An index array.

Used for. Rankings.

Reordered names.

doc_names[...]

Read as. Select or reorder names by indices.

Shape/return. A reordered array.

Used for. Document ranking.

Warning B.6.1. Sorted positions are not sorted scores.

np.argsort(scores) returns positions, not sorted scores.