大约有 43,100 项符合查询结果（耗时：0.0355秒） [XML]
Python assigning multiple variables to same value? list behavior
... and Chris Wallace have a hot dog. If you change the first element of a to 1, the first elements of b and c are 1.
If you want to know if two names are naming the same object, use the is operator:
>>> a=b=c=[0,3,5]
>>> a is b
True
You then ask:
what is different from this...
How to scale down a range of numbers with a known min and max value
...anel. I want the height and width of each ellipse to be in a range of say 1-30. I have methods that find the minimum and maximum values from my data set, but I won't have the min and max until runtime. Is there an easy way to do this?
...
What is the smallest possible valid PDF?
...
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....
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 ...
Get index of array element faster than O(n)
...
118
Convert the array into a hash. Then look for the key.
array = ['a', 'b', 'c']
hash = Hash[arr...
Disable migrations when running unit tests in Django 1.7
Django 1.7 introduced database migrations .
7 Answers
7
...
Command-line Unix ASCII-based charting / plotting tool
...
12 Answers
12
Active
...
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
...
Extract every nth element of a vector
...
163
a <- 1:120
b <- a[seq(1, length(a), 6)]
...