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Select first 4 rows of a data.frame in R
How can I select the first 4 rows of a data.frame :
5 Answers
5
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Why is WinRT unmanaged? [closed]
...e runtime implementation detail. The collector for .NET is very different from the collector for Javascript for example. The native objects created in either must observe the very strict rules of the collector. Which in turn means that they would have had to create WinRT versions that are specifi...
select、poll、epoll之间的区别总结[整理] - C/C++ - 清泛网 - 专注C/C++及内核技术
select、poll、epoll之间的区别总结[整理]select，poll，epoll都是IO多路复用的机制。I O多路复用就通过一种机制，可以监视多个描述符，一旦某个描述符就绪（一般是读就绪或者写就绪...select，poll，epoll都是IO多路复用的机制。I/O多路...
Ordering by the order of values in a SQL IN() clause
...
Use MySQL's FIELD() function:
SELECT name, description, ...
FROM ...
WHERE id IN([ids, any order])
ORDER BY FIELD(id, [ids in order])
FIELD() will return the index of the first parameter that is equal to the first parameter (other than the first paramet...
Play audio with Python
How can I play audio (it would be like a 1 second sound) from a Python script?
22 Answers
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Adding devices to team provisioning profile
...e.com
Add the UDID in devices
Go back to XCode, open up the Organizer and select "Provisioning Profiles", ensure that "Automatic Device Provisioning" is checked on the top right pane, then click on the "Refresh" button, and magically all your devices set in the provisioning portal will be automati...
Android adb “Unable to open sync connection!”
...t of the time. Then, seemingly randomly, when I try to run or debug my app from Eclipse, the Console in Eclipse says:
18 An...
How to drop columns by name in a data frame
..."z","u"))]
x y
1 1 2
2 2 3
3 3 4
4 4 5
5 5 6
Or, much simpler, use the select argument of the subset function : you can then use the - operator directly on a vector of column names, and you can even omit the quotes around the names !
R> subset(df, select=-c(z,u))
x y
1 1 2
2 2 3
3 3 4
4 4 ...
What GRANT USAGE ON SCHEMA exactly do?
...a schema doesn't grant rights on the tables within.
If you have rights to SELECT from a table, but not the right to see it in the schema that contains it then you can't access the table.
The rights tests are done in order:
Do you have `USAGE` on the schema?
No: Reject access.
Yes: Do...
T-SQL query to show table definition?
...n get most of the details from Information Schema Views and System Views.
SELECT ORDINAL_POSITION, COLUMN_NAME, DATA_TYPE, CHARACTER_MAXIMUM_LENGTH
, IS_NULLABLE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = 'Customers'
SELECT CONSTRAINT_NAME
FROM INFORMATION_SCHEMA.CONSTRAINT_TABLE_US...