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Numbering rows within groups in a data frame
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284
Use ave, ddply, dplyr or data.table:
df$num <- ave(df$val, df$cat, FUN = seq_along)
or:
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What exactly is the meaning of an API? [closed]
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edited Sep 16 '11 at 6:46
answered Sep 16 '11 at 5:56
us...
MySQL INSERT INTO table VALUES.. vs INSERT INTO table SET
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edited Jun 11 '12 at 7:14
answered May 14 '09 at 5:51
Vin...
上班狗来算算 你离财务自由还差多少钱？ - 杂谈 - 清泛网 - 专注C/C++及内核技术
...如果需要15万以上的现金年收入，则需要150万的本金。
C)终极版财务自由
这才是大BOSS~
如果你想实现终极版财务自由，这已经不是钱能计算出来的了，即便是胡润口中的1个亿，也不一定能让你达到终极版财务自由。
财务自由...
Docker - how can I copy a file from an image to a host?
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mit
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answered Jul 9 '15 at 11:51
Igor BukanovIgor Buk...
AttributeError: 'module' object has no attribute 'urlopen'
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254
This works in Python 2.x.
For Python 3 look in the docs:
import urllib.request
with urllib.re...
How to convert Java String into byte[]?
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edited Mar 31 '16 at 21:54
answered Sep 2 '13 at 10:46
Ste...
Excel RTD(Excel Real-Time Data)实时刷新数据技术 - C/C++ - 清泛网 - 专注C/C++及内核技术
Excel RTD(Excel Real-Time Data)实时刷新数据技术从Excel 2002开始，微软提供了一种叫做Excel RTD（real-time data）的技术，使用该技术可以在Excel中实时查看和更新数据。RTD采用所谓的...从Excel 2002开始，微软提供了一种叫做Excel RTD（real-time d...
Why not use exceptions as regular flow of control?
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How to make Eclipse behave well in the Windows 7 taskbar?
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answered Mar 14 '11 at 15:22
whlkwhlk
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