大约有 18,000 项符合查询结果（耗时：0.0492秒） [XML]
How to sort a dataframe by multiple column(s)
...ns. For example, with the data.frame below I would like to sort by column z (descending) then by column b (ascending):
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Defining an array of anonymous objects in CoffeeScript
... island205island205
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How to count TRUE values in a logical vector
...re some problems when logical vector contains NA values.
See for example:
z <- c(TRUE, FALSE, NA)
sum(z) # gives you NA
table(z)["TRUE"] # gives you 1
length(z[z == TRUE]) # f3lix answer, gives you 2 (because NA indexing returns values)
So I think the safest is to use na.rm = TRUE:
sum(z, na....
What characters are allowed in an email address?
...these ASCII characters:
uppercase and lowercase Latin letters A to Z and a to z;
digits 0 to 9;
special characters !#$%&'*+-/=?^_`{|}~;
dot ., provided that it is not the first or last character unless quoted, and provided also that it does not appear consecutively unless quoted (e...
How to test multiple variables against a value?
...omparison for all names here. You are looking for:
if x == 1 or y == 1 or z == 1:
x and y are otherwise evaluated on their own (False if 0, True otherwise).
You can shorten that using a containment test against a tuple:
if 1 in (x, y, z):
or better still:
if 1 in {x, y, z}:
using a set to ...
What is this date format? 2011-08-12T20:17:46.384Z
I have the following date: 2011-08-12T20:17:46.384Z . What format is this? I'm trying to parse it with Java 1.4 via DateFormat.getDateInstance().parse(dateStr) and I'm getting
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What does the 'Z' mean in Unix timestamp '120314170138Z'?
...
Yes. 'Z' stands for Zulu time, which is also GMT and UTC.
From http://en.wikipedia.org/wiki/Coordinated_Universal_Time:
The UTC time zone is sometimes denoted by the letter Z—a reference to
the equivalent nautical time zon...
Python UTC datetime object's ISO format doesn't include Z (Zulu or Zero offset)
Why python 2.7 doesn't include Z character (Zulu or zero offset) at the end of UTC datetime object's isoformat string unlike JavaScript?
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How to validate an email address using a regular expression?
...Scrape the rendered version, not the markdown, for actual code.)
(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z...
Minimum and maximum value of z-index?
...
http://www.w3.org/TR/CSS21/visuren.html#z-index
'z-index'
Value: auto | <integer> | inherit
http://www.w3.org/TR/CSS21/syndata.html#numbers
Some value types may have integer
values (denoted by <integer>) or
real number values (de...