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How to copy a collection from one database to another in MongoDB
...on for toying around with the shell. Plus, it would not bring over the indexes. If I was doing this, I would do the mongodump/mongorestore every time.
– Jason McCay
Jul 19 '12 at 6:18
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Very simple log4j2 XML configuration file using Console and File appender
I'd like a very simple XML configuration file with a console and a file appender using log4j2.
4 Answers
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推荐系统算法初探 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...阵，如下：
图中，行是不同的用户，列是所有物品，(x, y)的值则是x用户对y物品的评分（喜好程度）。我们可以把每一行视为一个用户对物品偏好的向量，然后计算每两个用户之间的向量距离，这里我们用余弦相似度来算：
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Programmatically get the cache line size?
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On Linux (with a reasonably recent kernel), you can get this information out of /sys:
/sys/devices/system/cpu/cpu0/cache/
This directory has a subdirectory for each level of cache. Each of those directories contains the followin...
Get all directories within directory nodejs
...10.0+
We can use the new withFileTypes option of readdirSync to skip the extra lstatSync call:
const { readdirSync } = require('fs')
const getDirectories = source =>
readdirSync(source, { withFileTypes: true })
.filter(dirent => dirent.isDirectory())
.map(dirent => dirent.name)...
How to send HTTP request in java? [duplicate]
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You can use java.net.HttpUrlConnection.
Example (from here), with improvements. Included in case of link rot:
public static String executePost(String targetURL, String urlParameters) {
HttpURLConnection connection = null;
try {
//Create connection
URL ...
Codesign error: Provisioning profile cannot be found after deleting expired profile
... an app that was working just yesterday. Got a message that a profile had expired, so I removed it from the iPod and from iTunes. When I chose a new profile (one with an * in the identifier), I now get an error:
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Equation (expression) parser with precedence?
...ive descent parser.
To get precedence you need to think recursively, for example, using your sample string,
1+11*5
to do this manually, you would have to read the 1, then see the plus and start a whole new recursive parse "session" starting with 11... and make sure to parse the 11 * 5 into its ...
How to check if a column exists in a SQL Server table?
I need to add a specific column if it does not exist. I have something like the following, but it always returns false:
31 ...
Improve INSERT-per-second performance of SQLite
...e used for your database.
If you have indices, consider calling CREATE INDEX after doing all your inserts. This is significantly faster than creating the index and then doing your inserts.
You have to be quite careful if you have concurrent access to SQLite, as the whole database is locked when writ...