大约有 16,000 项符合查询结果（耗时：0.0279秒） [XML]
Mean per group in a data.frame [duplicate]
...his type of operation is exactly what aggregate was designed for:
d <- read.table(text=
'Name Month Rate1 Rate2
Aira 1 12 23
Aira 2 18 73
Aira 3 19 45
Ben 1 53 19
Ben 2 22 87
Ben 3 19...
Getting root permissions on a file inside of vi? [closed]
...
Common Caveats
The most common method of getting around the read-only file problem is to open a pipe to current file as the super-user using an implementation of sudo tee. However, all of the most popular solutions that I have found around the Internet have a combination of a several...
In mongoDb, how do you remove an array element by its index?
...approach is not atomic and can cause some race conditions if other clients read and/or write between the two operations. If we need the operation to be atomic, we could:
Read the document from the database
Update the document and remove the item in the array
Replace the document in the database. T...
How can I replace every occurrence of a String in a file with PowerShell?
...-Content file.txt) is required:
Without the parenthesis the content is read, one line at a time, and flows down the pipeline until it reaches out-file or set-content, which tries to write to the same file, but it's already open by get-content and you get an error. The parenthesis causes the oper...
LPCSTR, LPCTSTR and LPTSTR
...string (const) | LPCSTR | LPCWSTR | LPCTSTR |
Bonus Reading
TCHAR → Text Char (archive.is)
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How do I read the contents of a Node.js stream into a string variable?
...what do you want me to do?)
The key is to use the data and end events of a Readable Stream. Listen to these events:
stream.on('data', (chunk) => { ... });
stream.on('end', () => { ... });
When you receive the data event, add the new chunk of data to a Buffer created to collect the data.
When ...
SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certificate verify failed
...
The command to do this is:
rvm install 2.2.0 --disable-binary
if you already have the version in question, you can re-install it with:
rvm reinstall 2.2.0 --disable-binary
(obviously, substitute your ruby version as needed).
...
MySQL Workbench: How to keep the connection alive
...-> SQL Editor and set to a higher value this parameter: DBMS connection read time out (in seconds). For instance: 86400.
Close and reopen MySQL Workbench. Kill your previously query that
probably is running and run the query again.
...
How do you get a list of the names of all files present in a directory in Node.js?
...
You can use the fs.readdir or fs.readdirSync methods.
fs.readdir
const testFolder = './tests/';
const fs = require('fs');
fs.readdir(testFolder, (err, files) => {
files.forEach(file => {
console.log(file);
});
});
fs.readdirS...
How to count number of files in each directory?
... the directories and let bash do the rest:
find . -type d -print0 | while read -d '' -r dir; do
files=("$dir"/*)
printf "%5d files in directory %s\n" "${#files[@]}" "$dir"
done
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