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Rails :dependent => :destroy VS :dependent => :delete_all
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The difference is with the callback.
The :delete_all is made directly in your application and deletes by SQL :
DELETE * FROM users where compagny_id = XXXX
With the :destroy, there is an instantiation of all of your children. So, if you can't destr...
How to get an array of specific “key” in multidimensional array without looping
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Since php 5.5, you can use array_column:
$ids = array_column($users, 'id');
This is the preferred option on any modern project. However, if you must support php > 5.5, the following alternatives exist:
Since php 5.3, you can use array_ma...
R programming: How do I get Euler's number?
...ession
exp(1)
represents e, and
exp(2)
represents e^2.
This works because exp is the exponentiation function with base e.
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git branch -d gives warning
...t to get a better understanding of the warning message after I deleted a local branch
4 Answers
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Skip rows during csv import pandas
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You can try yourself:
>>> import pandas as pd
>>> from StringIO import StringIO
>>> s = """1, 2
... 3, 4
... 5, 6"""
>>> pd.read_csv(StringIO(s), skiprows=[1], header=None)
0 1
0 1 2
1 ...
How to convert list of tuples to multiple lists?
...4, 6)]
The only difference is that you get tuples instead of lists. You can convert them to lists using
map(list, zip(*[(1, 2), (3, 4), (5, 6)]))
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When to use f:viewAction / preRenderView versus PostConstruct?
...bean's constructor. This will thus run only once per view, session or application when the bean is view, session or application scoped. The <f:viewAction> is by default only invoked on initial GET request, but can via onPostback="true" attribute be configured to be invoked on postback requests...
C# Convert List to Dictionary
...e first lambda lets you pick the key, the second one picks the value.
You can play with it and make values differ from the keys, like this:
var res = list.ToDictionary(x => x, x => string.Format("Val: {0}", x));
If your list contains duplicates, add Distinct() like this:
var res = list.Di...
Does constexpr imply inline?
...tions in C++11 required them to be simple enough that they were often good candidates for inline expansion (the primary exception being those that are recursive). Since then, however, the rules have gotten progressively looser, so constexpr can be applied to substantially larger, more complex functi...
How do I include related model fields using Django Rest Framework?
...t will only include relationships for forward relationships, which in this case isn't quite what you need, since the teachers field is a reverse relationship.
If you've got more complex requirements (eg. include reverse relationships, nest some fields, but not others, or nest only a specific subset...