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Should each and every table have a primary key?
...s, most RDBMS engines will benefit from including these fields in a unique index.
And since any primary key involves creating a unique index, you should declare it and get both logical consistency and performance.
See this article in my blog for why you should always create a unique index on uniqu...
Creating a zero-filled pandas data frame
...
You can try this:
d = pd.DataFrame(0, index=np.arange(len(data)), columns=feature_list)
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Using Ajax.BeginForm with ASP.NET MVC 3 Razor
...oller:
public class HomeController : Controller
{
public ActionResult Index()
{
return View(new MyViewModel());
}
[HttpPost]
public ActionResult Index(MyViewModel model)
{
return Content("Thanks", "text/html");
}
}
View:
@model AppName.Models.MyViewMo...
Pandas dataframe get first row of each group
...h
If you need id as column:
>>> df.groupby('id').first().reset_index()
id value
0 1 first
1 2 first
2 3 first
3 4 second
4 5 first
5 6 first
6 7 fourth
To get n first records, you can use head():
>>> df.groupby('id').head(2).reset_index(drop=Tru...
Access lapply index names inside FUN
Is there a way to get the list index name in my lapply() function?
12 Answers
12
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string.charAt(x) or string[x]?
...rks I did showed a three time decrease in performance when using charAt vs indexer in Chrome when the string is boxed in an object. I know that's not really relevant, but still worth noting.jsfiddle.net/mdasxxd2
– Siderite Zackwehdex
Jul 25 '16 at 10:51
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Combining multiple git repositories
...is uses git's filter-branch command):
$ cd phd/code
$ git filter-branch --index-filter \
'git ls-files -s | sed "s#\t#&code/#" |
GIT_INDEX_FILE=$GIT_INDEX_FILE.new \
git update-index --index-info &&
mv $GIT_INDEX_FILE.new $GIT_INDEX_FILE' HEAD
Same for the content of...
Laravel - Route::resource vs Route::controller
... Action Route Name
GET /users index users.index
GET /users/create create users.create
POST /users store users.store
GET /users/{user} show users.show
GET /user...
How can I define a composite primary key in SQL?
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SELECT * FROM voting WHERE QuestionID = 7
it will use the primary key's index. If however you do this:
SELECT * FROM voting WHERE MemberID = 7
it won't because to use a composite index requires using all the keys from the "left". If an index is on fields (A,B,C) and your criteria is on B and C...
postgresql list and order tables by size
...al_relation_size(<relation_name>) - gets total size of table and its index in bytes.
pg_relation_size(<relation_name>) - gets relation (table/index) size in bytes.
pg_index_size(<relation_name>) - gets index size of the relation in bytes.
current_database() - gets the currently ...