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Numbering rows within groups in a data frame
...
Use ave, ddply, dplyr or data.table:
df$num <- ave(df$val, 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 refere...
postgresql - replace all instances of a string within text field
...stance :
UPDATE <table> SET <field> = replace(<field>, 'cat', 'dog')
Be aware, though, that this will be a string-to-string replacement, so 'category' will become 'dogegory'. the regexp_replace function may help you define a stricter match pattern for what you want to replace.
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Throwing cats out of windows
Imagine you're in a tall building with a cat. The cat can survive a fall out of a low story window, but will die if thrown from a high floor. How can you figure out the longest drop that the cat can survive, using the least number of attempts?
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How do I create an abstract base class in JavaScript?
...error:
new Animal(); // throws
This is how you "inherit" from it:
var Cat = function() {
Animal.apply(this, arguments);
// Cat initialization...
};
Cat.prototype = Object.create(Animal.prototype);
Cat.prototype.constructor = Cat;
Cat.prototype.say = function() {
console.log('meow')...
How do I test an AngularJS service with Jasmine?
... of the service or factory. Angular uses this injector itself in your applications, too, to tell the application what is available.
However, it can be called in more than one place, and it can also be called implicitly instead of explicitly. You'll notice in my example spec test file below, the befo...
How to pipe list of files returned by find command to cat to view all the files
...nd then getting a list of files. How do I pipe it to another utility like cat (so that cat displays the contents of all those files) and basically need to grep something from these files.
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How to append contents of multiple files into one file
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You need the cat (short for concatenate) command, with shell redirection (>) into your output file
cat 1.txt 2.txt 3.txt > 0.txt
share
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How do I migrate a model out of one django app and into a new one?
...mon
| |-- migrations
| | |-- 0001_initial.py
| | `-- 0002_create_cat.py
| `-- models.py
`-- specific
|-- migrations
| |-- 0001_initial.py
| `-- 0002_create_dog.py
`-- models.py
Now we want to move model common.models.cat to specific app (precisely to specific.models...
How to avoid type safety warnings with Hibernate HQL results?
...elper
Simply refactor all your @SuppressWarnings into one place:
List<Cat> cats = MyHibernateUtils.listAndCast(q);
...
public static <T> List<T> listAndCast(Query q) {
@SuppressWarnings("unchecked")
List list = q.list();
return list;
}
Prevent Eclipse from generat...
Why is reading lines from stdin much slower in C++ than Python?
...wered Feb 21 '12 at 3:24
Vaughn CatoVaughn Cato
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