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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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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...
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...
Symbol for any number of any characters in regex?
I'm wondering is there a symbol for any number (including zero) of any characters
5 Answers
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Most efficient way to concatenate strings?
...gt; and other input types, with and without separators of different types (Char, String), but here I show the simple case of concatenating all strings in an array into a single string, with no separator. Latest version here is developed and unit-tested on C# 7 and .NET 4.7.
There are two keys to h...
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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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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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...
Dynamic SELECT TOP @var In SQL Server
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SELECT TOP (@count) * FROM SomeTable
This will only work with SQL 2005+
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Colorized Ruby output to the terminal [closed]
...tional:
def no_colors
self.gsub /\e\[\d+m/, ""
end
removes formatting characters
Note
puts "\e[31m" # set format (red foreground)
puts "\e[0m" # clear format
puts "green-#{"red".red}-green".green # will be green-red-normal, because of \e[0
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