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Convert column classes in data.table
...ng data.table: How do I convert column classes? Here is a simple example: With data.frame I don't have a problem converting it, with data.table I just don't know how:
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Why switch is faster than if
Lots of Java books describe the switch statement as being faster than the if else statement. But I did not find out anywhere why switch is faster than if .
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Remove last character of a StringBuilder?
...op through a collection and make a string of each data separated by a delimiter, you always end up with an extra delimiter at the end, e.g.
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Is there a Public FTP server to test upload and download? [closed]
... For download testing they provide fixed size files, you can choose which fits best to your test.
You can connect with username of anonymous and any password (e.g. anonymous ).
You can upload files to upload folder. You can't create new folder here.
Your file is deleted immediately after successful...
Android image caching
...true);
Object response = connection.getContent();
if (response instanceof Bitmap) {
Bitmap bitmap = (Bitmap)response;
}
Provides both memory and flash-rom cache, shared with the browser.
grr. I wish somebody had told ME that before i wrote my own cache manager.
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mysql_fetch_array()/mysql_fetch_assoc()/mysql_fetch_row()/mysql_num_rows etc… expects parameter 1 to
...ir respective query functions/methods. You need to test for that error condition and handle it accordingly.
mysql_* extension:
NOTE The mysql_ functions are deprecated and have been removed in php version 7.
Check $result before passing it to mysql_fetch_array. You'll find that it's false bec...
How to sum up elements of a C++ vector?
...
Actually there are quite a few methods.
int sum_of_elems = 0;
C++03
Classic for loop:
for(std::vector<int>::iterator it = vector.begin(); it != vector.end(); ++it)
sum_of_elems += *it;
Using a standard algorithm:
#include &l...
CSS background image to fit width, height should auto-scale in proportion
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There is a CSS3 property for this, namely background-size (compatibility check). While one can set length values, it's usually used with the special values contain and cover. In your specific case, you should use cover:
body {
background-image: url(images/background.svg);
backgroun...
How do I check if there are duplicates in a flat list?
For example, given the list ['one', 'two', 'one'] , the algorithm should return True , whereas given ['one', 'two', 'three'] it should return False .
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What are the differences between a clustered and a non-clustered index?
...red index
Both types of index will improve performance when select data with fields that use the index but will slow down update and insert operations.
Because of the slower insert and update clustered indexes should be set on a field that is normally incremental ie Id or Timestamp.
SQL Server w...