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Oracle “Partition By” Keyword
Can someone please explain what the partition by keyword does and give a simple example of it in action, as well as why one would want to use it? I have a SQL query written by someone else and I'm trying to figure out what it does.
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How to map with index in Ruby?
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If you're using ruby 1.8.7 or 1.9, you can use the fact that iterator methods like each_with_index, when called without a block, return an Enumerator object, which you can call Enumerable methods like map on. So you can do:
arr.each_with_inde...
How to print a groupby object
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Simply do:
grouped_df = df.groupby('A')
for key, item in grouped_df:
print(grouped_df.get_group(key), "\n\n")
This also works,
grouped_df = df.groupby('A')
gb = grouped_df.groups
for key, values in gb.iteritems():
print(df.ix[values], "\n\n...
Java generics - why is “extends T” allowed but not “implements T”?
... Java for using always " extends " rather than " implements " for defining bounds of typeparameters.
8 Answers
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bash: shortest way to get n-th column of output
...dly encounter the following form of columnized output from some command in bash (in my case from executing svn st in my Rails working directory):
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Is it possible to assign numeric value to an enum in Java?
Is anything like this possible in Java? Can one assign custom numeric values to enum elements in Java?
5 Answers
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Can I call a constructor from another constructor (do constructor chaining) in C++?
... constructors).
The syntax is slightly different from C#:
class Foo {
public:
Foo(char x, int y) {}
Foo(int y) : Foo('a', y) {}
};
C++03: No
Unfortunately, there's no way to do this in C++03, but there are two ways of simulating this:
You can combine two (or more) constructors via defau...
In javascript, is an empty string always false as a boolean?
... of ECMAScript, and ECMAScript language specification clearly defines this behavior:
ToBoolean
The result is false if the argument is the empty String (its length is zero);
otherwise the result is true
Quote taken from http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-262.pdf
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Propagate all arguments in a bash shell script
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Use "$@" instead of plain $@ if you actually wish your parameters to be passed the same.
Observe:
$ cat foo.sh
#!/bin/bash
baz.sh $@
$ cat bar.sh
#!/bin/bash
baz.sh "$@"
$ cat baz.sh
#!/bin/bash
echo Received: $1
echo Received: $2
echo Received: $3
echo Received: $4
$ ./foo.sh first secon...
Why exactly is eval evil?
I know that Lisp and Scheme programmers usually say that eval should be avoided unless strictly necessary. I’ve seen the same recommendation for several programming languages, but I’ve not yet seen a list of clear arguments against the use of eval . Where can I find an account of the potentia...