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Diffstat (limited to 'Doc/lib/libitertools.tex')
| -rw-r--r-- | Doc/lib/libitertools.tex | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/Doc/lib/libitertools.tex b/Doc/lib/libitertools.tex index ac6028b..e2f0f0e 100644 --- a/Doc/lib/libitertools.tex +++ b/Doc/lib/libitertools.tex @@ -138,6 +138,13 @@ by functions or loops that truncate the stream. identity function and returns the element unchanged. Generally, the iterable needs to already be sorted on the same key function. + The operation of \function{groupby()} is similar to the \code{uniq} filter + in \UNIX{}. It generates a break or new group every time the value + of the key function changes (which is why it is usually necessary + to have sorted the data using the same key function). That behavior + differs from SQL's GROUP BY which aggregates common elements regardless + of their input order. + The returned group is itself an iterator that shares the underlying iterable with \function{groupby()}. Because the source is shared, when the \function{groupby} object is advanced, the previous group is no @@ -147,6 +154,7 @@ by functions or loops that truncate the stream. \begin{verbatim} groups = [] uniquekeys = [] + data = sorted(data, key=keyfunc) for k, g in groupby(data, keyfunc): groups.append(list(g)) # Store group iterator as a list uniquekeys.append(k) |