大约有 47,000 项符合查询结果（耗时：0.0409秒） [XML]
dplyr summarise: Equivalent of “.drop=FALSE” to keep groups with zero length in output
...
Since dplyr 0.8 group_by gained the .drop argument that does just what you asked for:
df = data.frame(a=rep(1:3,4), b=rep(1:2,6))
df$b = factor(df$b, levels=1:3)
df %>%
group_by(b, .drop=FALSE) %>%
summarise(count_a=length(a)...
ActiveRecord: size vs count
...
|
edited Jul 10 '12 at 22:15
Jo Liss
22.5k1414 gold badges101101 silver badges150150 bronze badges
...
Fastest way to remove first char in a String
... |
edited Jul 11 '10 at 7:02
answered Jul 11 '10 at 6:44
...
Accessing class variables from a list comprehension in the class definition
...owing will fail:
class A:
a = 42
b = list(a + i for i in range(10))
So, to summarize: you cannot access the class scope from functions, list comprehensions or generator expressions enclosed in that scope; they act as if that scope does not exist. In Python 2, list comprehensions were i...
How to format strings in Java
...
140
In addition to String.format, also take a look java.text.MessageFormat. The format less terse a...
Quickest way to convert a base 10 number to any base in .NET?
...s binary representation
Console.WriteLine(binary); // prints 101
However, as pointed out by the comments, Convert.ToString only supports the following limited - but typically sufficient - set of bases: 2, 8, 10, or 16.
Update (to meet the requirement to convert to any base):
I'm no...
~x + ~y == ~(x + y) is always false?
...
|
edited Jun 20 '12 at 13:47
answered Jun 20 '12 at 2:35
...
Checking images for similarity with OpenCV
...ue (maybe a percentage) that indicates how similar these images are? E.g. 100% would be returned if the same image was passed twice, 0% would be returned if the images were totally different.
...
Putting text in top left corner of matplotlib plot
...t is in data coords,
alternatively, you can specify text in axis coords (0,0 is lower-left
and 1,1 is upper-right). The example below places text in the center
of the axes::
text(0.5, 0.5,'matplotlib',
horizontalalignment='center',
verticalalignment='center',
transform = ax.t...
Sort array of objects by single key with date value
... use Array.sort.
Here's an example:
var arr = [{
"updated_at": "2012-01-01T06:25:24Z",
"foo": "bar"
},
{
"updated_at": "2012-01-09T11:25:13Z",
"foo": "bar"
},
{
"updated_at": "2012-01-05T04:13:24Z",
"foo": "bar"
}
]
arr.sort(function(a, b) {
v...