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What is the difference between JOIN and UNION?
...mpletely different operations. Trivial example of UNION:
mysql> SELECT 23 AS bah
-> UNION
-> SELECT 45 AS bah;
+-----+
| bah |
+-----+
| 23 |
| 45 |
+-----+
2 rows in set (0.00 sec)
similary trivial example of JOIN:
mysql> SELECT * FROM
-> (SELECT 23 AS bah) AS fo...
How to initialize a dict with keys from a list and empty value in Python?
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dict.fromkeys([1, 2, 3, 4])
This is actually a classmethod, so it works for dict-subclasses (like collections.defaultdict) as well. The optional second argument specifies the value to use for the keys (defaults to None.)
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Homebrew install specific version of formula?
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What's the best way to parse command line arguments? [closed]
...ggests optparse which is appropriate for older Python versions. For Python 2.7 and above, argparse replaces optparse. See this answer for more information.
As other people pointed out, you are better off going with optparse over getopt. getopt is pretty much a one-to-one mapping of the standard ge...
Closure in Java 7 [closed]
...e pioneers introducing closures in Java. His post on closures from January 28, 2007 is named A Definition of Closures On his blog there is lots of information to get you started as well as videos. An here is an excellent Google talk - Advanced Topics In Programming Languages - Closures For Java with...
do { … } while (0) — what is it good for? [duplicate]
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edited Nov 3 '08 at 9:24
answered Nov 2 '08 at 21:40
Gr...
Error :: duplicate files during packaging of APK
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answered Mar 18 '14 at 5:25
Xavier DucrohetXavier Ducrohet
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Dynamically Changing log4j log level
...runtime does not persist the level change.
UPDATE: If you are using Log4j 2 you should remove the calls to setLevel per the documentation as this can be achieved via implementation classes.
Calls to logger.setLevel() or similar methods are not supported in the
API. Applications should remove ...
Grep for literal strings
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answered Jul 14 '10 at 2:08
Scott StaffordScott Stafford
38.9k2020 gold badges110110 silver badges158158 bronze badges
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Pandas DataFrame Groupby two columns and get counts
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126
Followed by @Andy's answer, you can do following to solve your second question:
In [56]: df.gr...