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Aggregate / summarize multiple variables per group (e.g. sum, mean)
...[, lapply(.SD, sum), by=.(year, month), .SDcols=c("x1","x2")]
setDF(df2) # convert back to dataframe
Using the plyr package
require(plyr)
df2 <- ddply(df1, c("year", "month"), function(x) colSums(x[c("x1", "x2")]))
Using summarize() from the Hmisc package
(column headings are messy in my ex...
Java - escape string to prevent SQL injection
...e the "replaceAll" string function. Ultimately I need a function that will convert any existing \ to \\ , any " to \" , any ' to \' , and any \n to \\n so that when the string is evaluated by MySQL SQL injections will be blocked.
...
Sending multipart/formdata with jQuery.ajax
...ust leave the processData flag set to false, otherwise, jQuery will try to convert your FormData into a string, which will fail.
You may now retrieve the file in PHP using:
$_FILES['file-0']
(There is only one file, file-0, unless you specified the multiple attribute on your file input, in which...
Debugging automatic properties
Is there any way to set breakpoint on setter/getter in auto-implemented property?
5 Answers
...
Sending a message to nil in Objective-C
...sing a very contrived example. Let's say you have a method in Java which prints out all of the elements in an ArrayList:
void foo(ArrayList list)
{
for(int i = 0; i < list.size(); ++i){
System.out.println(list.get(i).toString());
}
}
Now, if you call that method like so: someOb...
Why do objects of the same class have access to each other's private data?
...t compile time. Only per-class control can be implemented that way.
Some hints of per-object control are present in protected access specification, which is why it even has its own dedicated chapter in the standard (11.5). But still any per-object features described there are rather rudimentary. Ag...
What are static factory methods?
...d providing direct access to database connections because they're resource intensive. So we use a static factory method getDbConnection that creates a connection if we're below the limit. Otherwise, it tries to provide a "spare" connection, failing with an exception if there are none.
public class...
SELECT DISTINCT on one column
...ow has all shown), this is the correct query:
declare @TestData table (ID int, sku char(6), product varchar(15))
insert into @TestData values (1 , 'FOO-23' ,'Orange')
insert into @TestData values (2 , 'BAR-23' ,'Orange')
insert into @TestData values (3 , 'FOO-24' ,'Apple')
insert ...
Stateless and Stateful Enterprise Java Beans
...ually should show that user1 has 1 and user2 has 1 ( if thats what you are intending to do. Shopping cart example as above).
– Krishna
Aug 19 '13 at 16:48
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...
What is the use of the pipe symbol in YAML?
...dicates that multi-line "folded" scalar follows, meaning that newlines are converted to spaces. For example:
>>> import yaml
>>> yaml.load("""
... |
... This is a multi-line
... literal style scalar.
... """)
'This is a multi-line\nliteral style scalar.\n'
>>> yaml.loa...