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Numbering rows within groups in a data frame
...l, df$cat, FUN = seq_along)
or:
library(plyr)
ddply(df, .(cat), mutate, id = seq_along(val))
or:
library(dplyr)
df %>% group_by(cat) %>% mutate(id = row_number())
or (the most memory efficient, as it assigns by reference within DT):
library(data.table)
DT <- data.table(df)
DT[, id...
Sequelize Unknown column '*.createdAt' in 'field list'
..., which creates the following query:
SELECT `users`.*, `userDetails`.`userId` AS `userDetails.userId`,`userDetails`.`firstName` AS `userDetails.firstName`,`userDetails`.`lastName` AS `userDetails.lastName`, `userDetails`.`birthday` AS `userDetails.birthday`, `userDetails`.`id` AS `userDetails.id`, ...
NULL vs nil in Objective-C
...
nil should only be used in place of an id, what we Java and C++ programmers would think of as a pointer to an object. Use NULL for non-object pointers.
Look at the declaration of that method:
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object...
How do you specify that a class property is an integer?
...rimenting with TypeScript, and in the process of creating a class with an "ID" field that should be an integer, I have gotten a little confused.
...
What are best practices for REST nested resources?
As far as I can tell each individual resource should have only one canonical path. So in the following example what would good URL patterns be?
...
jQuery UI Dialog with ASP.NET button postback
...true,
show: 'Transfer',
hide: 'Transfer',
width: 320,
autoOpen: false,
minHeight: 10,
minwidth: 10
});
dlg.parent().appendTo(...
Tying in to Django Admin's Model History
...min.models import LogEntry, ADDITION
LogEntry.objects.log_action(
user_id = request.user.pk,
content_type_id = ContentType.objects.get_for_model(object).pk,
object_id = object.pk,
object_repr = force_unicode(object),
action_flag = ADDITION
)
where object...
How to choose the id generation strategy when using JPA and Hibernate
I was going through Id generation section of the Hibernate reference guide and "java persistence with Hibernate"
4 Answers
...
@UniqueConstraint and @Column(unique = true) in hibernate annotation
...
As said before, @Column(unique = true) is a shortcut to UniqueConstraint when it is only a single field.
From the example you gave, there is a huge difference between both.
@Column(unique = true)
@ManyToOne(optional = false, fet...
What is DOM Event delegation?
...ion will continue up to and
including the Document.
Event bubbling provides the foundation for event delegation in browsers. Now you can bind an event handler to a single parent element, and that handler will get executed whenever the event occurs on any of its child nodes (and any of their chil...