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Drop data frame columns by name
...op=FALSE to keep R from converting your data frame to a vector if you only select a single column. Don't forget that data frames are lists, so list selection (one-dimensional like I did) works perfectly well and always returns a list. Or a data frame in this case, which is why I prefer to use it.
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SQL select join: is it possible to prefix all columns as 'prefix.*'?
... if this is possible in SQL. Say you have two tables A and B, and you do a select on table A and join on table B:
22 Answer...
How to get the Full file path from URI
...but if i do it like the MediaStore Solution, it won't work if the app user selects eg Astro as browser, instead of Music Player. How do I solve this?
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SQL ON DELETE CASCADE, Which Way Does the Deletion Occur?
...ould restructure your schema into this,
CREATE TABLE Categories
(
Code CHAR(4) NOT NULL PRIMARY KEY,
CategoryName VARCHAR(63) NOT NULL UNIQUE
);
CREATE TABLE Courses
(
CourseID INT NOT NULL PRIMARY KEY,
BookID INT NOT NULL,
CatCode CHAR(4) NOT NULL,
CourseNum CHAR(3) NOT NULL,
Cour...
Naming convention for unique constraint
...imary key doesn't get a sequence number since there can be only one. The 2-char alpha suffix meanings are:
PK: Primary Key
AK: Alternate Key
FK: Foreign Key
IX: IndeX
CK: ChecK
DF: DeFault
I generally want to group metadata/system catalog data by the controlling object rather than by object type...
How to find out client ID of component for ajax update/render? Cannot find component with expression
... <ui:repeat>.
When using PrimeFaces, consider Search Expressions or Selectors
PrimeFaces Search Expressions allows you to reference components via JSF component tree search expressions. JSF has several builtin:
@this: current component
@form: parent UIForm
@all: entire document
@none: noth...
How can I combine hashes in Perl?
...y ...)
See also
PM post on merging hashes
PM Categorical Q&A hash union
Perl Cookbook 5.10. Merging Hashes
websearch://perlfaq "merge two hashes"
websearch://perl merge hash
https://metacpan.org/pod/Hash::Merge
Footnotes
1 * (aka associative-array, aka dictionary)
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How to automatically remove trailing whitespace in Visual Studio 2008?
...
You can do this easily with these three actions:
Ctrl + A (select all text)
Edit -> Advanced -> Delete Horizontal Whitespace
Edit -> Advanced -> Format Selection
Wait a few seconds and done.
It's Ctrl + Z'able in case something went wrong.
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What kind of leaks does automatic reference counting in Objective-C not prevent or minimize?
...Core Foundation objects and memory allocated using malloc() for types like char*. ARC does not manage these types, only Objective-C objects, so you'll still need to deal with them yourself. Core Foundation types can be particularly tricky, because sometimes they need to be bridged across to matchi...
Meaning of $? (dollar question mark) in shell scripts
...k() == 0) {
/* Call false. */
execl("./false", "./false", (char *)NULL);
}
int status;
/* Wait for a child to finish. */
wait(&status);
/* Status encodes multiple fields,
* we need WEXITSTATUS to get the exit status:
* http://stackoverflow.com/questi...