大约有 43,100 项符合查询结果（耗时：0.0366秒） [XML]
What is the smallest possible valid PDF?
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198
This is an interesting problem. Taking it by the book, you can start off with this:
%PDF-1.0...
Aggregate / summarize multiple variables per group (e.g. sum, mean)
...he reshape2 package for this task:
require(reshape2)
df_melt <- melt(df1, id = c("date", "year", "month"))
dcast(df_melt, year + month ~ variable, sum)
# year month x1 x2
1 2000 1 -80.83405 -224.9540159
2 2000 2 -223.76331 -288.2418017
3 2000 3 -188.83930 -481....
Extract every nth element of a vector
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163
a <- 1:120
b <- a[seq(1, length(a), 6)]
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C语言面试那些事儿──一道指针与数组问题 - c++1y / stl - 清泛IT社区，为创新赋能！
...下代码：
int main(int argc, char** argv)
{
int a[5] = {1,2,3,4,5};
int* ptr = (int*)(&a + 1);
printf("%d,%d\n", *(a+1), *(ptr-1));
return 0;
}复制代码这道题在很多所谓经典C语言面试题里是常见的不能再...
Get index of array element faster than O(n)
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118
Convert the array into a hash. Then look for the key.
array = ['a', 'b', 'c']
hash = Hash[arr...
PostgreSQL Crosstab Query
...nce per database, which provides the function crosstab(). Since Postgres 9.1 you can use CREATE EXTENSION for that:
CREATE EXTENSION IF NOT EXISTS tablefunc;
Improved test case
CREATE TABLE tbl (
section text
, status text
, ct integer -- "count" is a reserved word in standard ...
Disable migrations when running unit tests in Django 1.7
Django 1.7 introduced database migrations .
7 Answers
7
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Command-line Unix ASCII-based charting / plotting tool
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12 Answers
12
Active
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Does Java 8 provide a good way to repeat a value or function?
...lue or function multiple times, eg. to get a list of 8 copies of the value 1:
5 Answers
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