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Why doesn't String switch statement support a null case?
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According to Java Docs:
A switch works with the byte, short, char, and int primitive data
types. It also works with enumerated types (discussed in Enum Types),
the String class, and a few special classes that wrap certain
primitive types: Character, Byte, Short, and Integer (disc...
Select multiple columns in data.table by their numeric indices
How can we select multiple columns using a vector of their numeric indices (position) in data.table ?
5 Answers
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Objective-C: Reading a file line by line
...hen scan for newlines (or whatever other delimiter) and save any remaining characters for the next read, or read more characters if a newline hasn't been read yet. (NSFileHandle lets you read an NSData which you can then convert to an NSString, but it's essentially the same process.)
Apple has a St...
When should I use double or single quotes in JavaScript?
... option, new in ECMAScript 6, is template literals which use the backtick character:
alert(`Use "double" and 'single' quotes in the same string`);
alert(`Escape the \` back-tick character and the \${ dollar-brace sequence in a string`);
Template literals offer a clean syntax for: variable interpol...
How to find the Number of CPU Cores via .NET/C#?
...ors:
foreach (var item in new System.Management.ManagementObjectSearcher("Select * from Win32_ComputerSystem").Get())
{
Console.WriteLine("Number Of Physical Processors: {0} ", item["NumberOfProcessors"]);
}
Cores:
int coreCount = 0;
foreach (var item in new System.Management.ManagementObjec...
typecast string to integer - Postgres
...ur value is an empty string, you can use NULLIF to replace it for a NULL:
SELECT
NULLIF(your_value, '')::int
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Reshaping data.frame from wide to long format
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Here is another example showing the use of gather from tidyr. You can select the columns to gather either by removing them individually (as I do here), or by including the years you want explicitly.
Note that, to handle the commas (and X's added if check.names = FALSE is not set), I am also us...
Finding duplicate values in MySQL
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Do a SELECT with a GROUP BY clause. Let's say name is the column you want to find duplicates in:
SELECT name, COUNT(*) c FROM table GROUP BY name HAVING c > 1;
This will return a result with the name value in the first colum...
Dump a mysql database to a plaintext (CSV) backup from the command line
... separated) files which can import into Excel, etc, quite easily:
% echo 'SELECT * FROM table' | mysql -B -uxxx -pyyy database
Alternatively, if you've got direct access to the server's file system, use SELECT INTO OUTFILE which can generate real CSV files:
SELECT * INTO OUTFILE 'table.csv'
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Ruby Arrays: select(), collect(), and map()
...re, to check the :qty key, you'd do something like the following:
details.select{ |item| item[:qty] != "" }
That will give you all items where the :qty key isn't an empty string.
official select documentation
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