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Update MongoDB field using value of another field
..."name": { "$concat": ["$firstName", " ", "$lastName"]}}}
]
)
MongoDB 3.4+
In 3.4+ you can use $addFields and the $out aggregation pipeline operators.
db.collection.aggregate(
[
{ "$addFields": {
"name": { "$concat": [ "$firstName", " ", "$lastName" ] }
}},
...
What exactly is Arel in Rails 3.0?
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What exactly is Arel in Rails 3.0?
It's an object model for an algebra of relational query operators.
I understand that it is a replacement for ActiveRecord
No, it isn't. It's a replacement for hand-crafting SQL queries in strings. It is a common query...
PyCharm shows unresolved references error for valid code
...Dmitry Trofimov
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3
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App Inventor 2开发计步器与定位器 - App Inventor 2 中文网 - 清泛IT论坛，有思想、有深度
...2.了解数据持久化，掌握数据存储等功能的实现；
3.通过编程实践，感受和体验利用手机自身硬件开发实用的手机应用程序。 【项目范例】
1. 情境
现在的手机都已经具有计步器及位置传感器等各种硬件传感...
How can I extract all values from a dictionary in Python?
I have a dictionary d = {1:-0.3246, 2:-0.9185, 3:-3985, ...} .
11 Answers
11
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jQuery Tips and Tricks
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share
edited Mar 23 '11 at 18:51
community wiki
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How to change Android Studio's editor font?
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32
Thanks, that worked. Not very intuitive UX, generally you save something after you have edited it, not before! I'll accept once it lets m...
Unicode与UTF-8互转(C语言实现) - C/C++ - 清泛网 - 专注C/C++及内核技术
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ASCII码一共规定了128个字符的编码, 比如空格"SPACE"是32(二进制00100000), 大写的
字母A是65(二进制01000001). 这128个符号(包括32个不能打印出来的控制符号), 只占用
了一个字节的后面7位, 最前面的1位统一规定为0.
1.2 非ASCII编码
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How can I represent an infinite number in Python?
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In Python, you can do:
test = float("inf")
In Python 3.5, you can do:
import math
test = math.inf
And then:
test > 1
test > 10000
test > x
Will always be true. Unless of course, as pointed out, x is also infinity or "nan" ("not a number").
Additionally (Python 2...
Fastest way to replace NAs in a large data.table
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system.time(a_gdata = f_gdata(dt1))
user system elapsed
18.805 12.301 134.985
system.time(a_andrie = f_andrie(dt1))
Error: cannot allocate vector of size 305.2 Mb
Timing stopped at: 14.541 7.764 68.285
system.time(f_dowle(dt1))
user system elapsed
7.452 4.144 19.590 # EDIT h...