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Pandas: create two new columns in a dataframe with values calculated from a pre-existing column
... from pandas import *
In [2]: def calculate(x):
...: return x*2, x*3
...:
In [3]: df = DataFrame({'a': [1,2,3], 'b': [2,3,4]})
In [4]: df
Out[4]:
a b
0 1 2
1 2 3
2 3 4
In [5]: df["A1"], df["A2"] = zip(*df["a"].map(calculate))
In [6]: df
Out[6]:
a b A1 A2
0 1 2 2...
Python - Create list with numbers between 2 values?
...t returns a list so all you need is:
>>> range(11, 17)
[11, 12, 13, 14, 15, 16]
In Python 3.x range is a iterator. So, you need to convert it to a list:
>>> list(range(11, 17))
[11, 12, 13, 14, 15, 16]
Note: The second number is exclusive. So, here it needs to be 16+1 = 17
E...
Why are Python lambdas useful? [closed]
...where you can pass functions to other functions to do stuff. Example:
mult3 = filter(lambda x: x % 3 == 0, [1, 2, 3, 4, 5, 6, 7, 8, 9])
sets mult3 to [3, 6, 9], those elements of the original list that are multiples of 3. This is shorter (and, one could argue, clearer) than
def filterfunc(x):
...
How to convert a scala.List to a java.util.List?
...ort scala.collection.jcl.ArrayList
unconvertList(new ArrayList ++ List(1,2,3))
From Scala 2.8 onwards:
import scala.collection.JavaConversions._
import scala.collection.mutable.ListBuffer
asList(ListBuffer(List(1,2,3): _*))
val x: java.util.List[Int] = ListBuffer(List(1,2,3): _*)
However, asLis...
Pickle incompatibility of numpy arrays between Python 2 and 3
I am trying to load the MNIST dataset linked here in Python 3.2 using this program:
7 Answers
...
How to swap keys and values in a hash
... (in essence, by letting you access keys through values):
{a: 1, b: 2, c: 3}.key(1)
=> :a
If you want to keep the inverted hash, then Hash#invert should work for most situations:
{a: 1, b: 2, c: 3}.invert
=> {1=>:a, 2=>:b, 3=>:c}
BUT...
If you have duplicate values, invert will...
Removing duplicates in lists
...ample should cover whatever you are trying to do:
>>> t = [1, 2, 3, 1, 2, 5, 6, 7, 8]
>>> t
[1, 2, 3, 1, 2, 5, 6, 7, 8]
>>> list(set(t))
[1, 2, 3, 5, 6, 7, 8]
>>> s = [1, 2, 3]
>>> list(set(t) - set(s))
[8, 5, 6, 7]
As you can see from the example resu...
No secret option provided to Rack::Session::Cookie warning?
I am running Rails 3.2.3, Ruby 1.9 under Fedora 17. I get this warning, when I run rails s , and how do I fix?
7 Answers
...
[] and {} vs list() and dict(), which is better?
...gt;> from timeit import timeit
>>> timeit("[]")
0.040084982867934334
>>> timeit("list()")
0.17704233359267718
>>> timeit("{}")
0.033620194745424214
>>> timeit("dict()")
0.1821558326547077
and for non-empty:
>>> timeit("[1,2,3]")
0.24316302770330367
...