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How to copy a dictionary and only edit the copy
.... If you want a deep copy, copy.deepcopy(dict1) is required. An example:
>>> source = {'a': 1, 'b': {'m': 4, 'n': 5, 'o': 6}, 'c': 3}
>>> copy1 = x.copy()
>>> copy2 = dict(x)
>>> import copy
>>> copy3 = copy.deepcopy(x)
>>> source['a'] = 10 # a...
How to do an update + join in PostgreSQL?
...ATE [ ONLY ] table [ [ AS ] alias ]
SET { column = { expression | DEFAULT } |
( column [, ...] ) = ( { expression | DEFAULT } [, ...] ) } [, ...]
[ FROM from_list ]
[ WHERE condition | WHERE CURRENT OF cursor_name ]
[ RETURNING * | output_expression [ [ AS ] output_name ] [...
“Cloning” row or column vectors
...
Here's an elegant, Pythonic way to do it:
>>> array([[1,2,3],]*3)
array([[1, 2, 3],
[1, 2, 3],
[1, 2, 3]])
>>> array([[1,2,3],]*3).transpose()
array([[1, 1, 1],
[2, 2, 2],
[3, 3, 3]])
the problem with [16] seems to be t...
What does the `forall` keyword in Haskell/GHC do?
...
Let's start with a code example:
foob :: forall a b. (b -> b) -> b -> (a -> b) -> Maybe a -> b
foob postProcess onNothin onJust mval =
postProcess val
where
val :: b
val = maybe onNothin onJust mval
This code doesn't compile (syntax error)...
How can I sort a dictionary by key?
... Dictionaries themselves do not have ordered items as such -> no longer true!
– minexew
Apr 6 at 6:46
...
Why does “return list.sort()” return None, not the list?
... integers named l the list itself will be reordered if we call l.sort():
>>> l = [1, 5, 2341, 467, 213, 123]
>>> l.sort()
>>> l
[1, 5, 123, 213, 467, 2341]
This method has no return value. But what if we try to assign the result of l.sort()?
>>> l = [1, 5, 234...
How would you make a comma-separated string from a list of strings?
...
Why the map/lambda magic? Doesn't this work?
>>> foo = ['a', 'b', 'c']
>>> print(','.join(foo))
a,b,c
>>> print(','.join([]))
>>> print(','.join(['a']))
a
In case if there are numbers in the list, you could use list comprehension:
...
Why does X[Y] join of data.tables not allow a full outer join, or a left join?
...lly followed by a subset?
If you want a left outer join of X[Y]
le <- Y[X]
mallx <- merge(X, Y, all.x = T)
# the column order is different so change to be the same as `merge`
setcolorder(le, names(mallx))
identical(le, mallx)
# [1] TRUE
If you want a full outer join
# the unique valu...
How to get an absolute file path in Python
...
>>> import os
>>> os.path.abspath("mydir/myfile.txt")
'C:/example/cwd/mydir/myfile.txt'
Also works if it is already an absolute path:
>>> import os
>>> os.path.abspath("C:/example/cwd/myd...
How to add to an existing hash in Ruby
In regards to adding an key => value pair to an existing populated hash in Ruby, I'm in the process of working through Apress' Beginning Ruby and have just finished the hashes chapter.
...