大约有 44,000 项符合查询结果（耗时：0.0566秒） [XML]
Aggregate / summarize multiple variables per group (e.g. sum, mean)
...-date), sum)
# summarising a specific set of non-grouping variables using select_helpers
# see ?select_helpers for more options
df2 <- df1 %>% group_by(year, month) %>% summarise_at(vars(starts_with('x')), sum)
df2 <- df1 %>% group_by(year, month) %>% summarise_at(vars(matches('.*...
iPhone App Minus App Store?
...w the use of this certificate:
Launch Keychain Access.app. With no items selected, from the Keychain menu select Certificate Assistant, then Create a Certificate.
Name: iPhone Developer
Certificate Type: Code Signing
Let me override defaults: Yes
Click Continue
Validity: 3650 days
Click Contin...
Getting back old copy paste behaviour in tmux, with mouse
... -g mode-mouse off
set-option -g mouse-resize-pane off
set-option -g mouse-select-pane off
set-option -g mouse-select-window off
# toggle mouse mode to allow mouse copy/paste
# set mouse on with prefix m
bind m \
set -g mode-mouse on \;\
set -g mouse-resize-pane on \;\
set -g mouse-selec...
Fastest way to check if a file exist using standard C++/C++11/C?
...r. This does not use many fancy features of C++:
bool is_file_exist(const char *fileName)
{
std::ifstream infile(fileName);
return infile.good();
}
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mongo group query how to keep fields
...t suggestions]
I came here looking for an answer but wasn't happy with the selected answer (especially given it's age). I found this answer that is a better solution (adapted):
db.test.aggregate({
$group: {
_id: '$name',
person: { "$first": "$$ROOT" },
count: { $sum: 1 }
},
{
"$r...
Sublime Text 2 and 3: open the same file multiple times
... the file in.
Type Ctrl-p (Mac: ⌘-p) to get the list of files available.
Select the one you're after and it will be loaded into the current pane
(Even if it's already open in another pane.)
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Hidden features of Perl?
...
One of my favourite features in Perl is using the boolean || operator to select between a set of choices.
$x = $a || $b;
# $x = $a, if $a is true.
# $x = $b, otherwise
This means one can write:
$x = $a || $b || $c || 0;
to take the first true value from $a, $b, and $c, or a default of 0...
How do I calculate tables size in Oracle
...BLE_NAME FORMAT A32
COLUMN OBJECT_NAME FORMAT A32
COLUMN OWNER FORMAT A10
SELECT
owner,
table_name,
TRUNC(sum(bytes)/1024/1024) Meg,
ROUND( ratio_to_report( sum(bytes) ) over () * 100) Percent
FROM
(SELECT segment_name table_name, owner, bytes
FROM dba_segments
WHERE segment_type IN...
Fix code indentation in Xcode
...
Before Xcode 9 (for Xcode 9 see default shortcut below)
select text
right-click
there's a "Re-indent selection" item in popup menu
In XCode 4 there is one more step:
select text
right-click
Click on "Structure"
there's a "Re-indent selection" and other options in popup men...
Entity Framework: table without primary key
...mn as a primary key, use NULLIF.
An easy way to apply this is to wrap the select statement of your view in another select.
Example:
SELECT
ISNULL(MyPrimaryID,-999) MyPrimaryID,
NULLIF(AnotherProperty,'') AnotherProperty
FROM ( ... ) AS temp
answered Apr 26 '10 at 17:00 by Tillito
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