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What does -1 mean in numpy reshape?
...inal shape'
numpy allow us to give one of new shape parameter as -1 (eg: (2,-1) or (-1,3) but not (-1, -1)). It simply means that it is an unknown dimension and we want numpy to figure it out. And numpy will figure this by looking at the 'length of the array and remaining dimensions' and making su...
How to drop columns by name in a data frame
... or the subset function. For example :
R> df <- data.frame(x=1:5, y=2:6, z=3:7, u=4:8)
R> df
x y z u
1 1 2 3 4
2 2 3 4 5
3 3 4 5 6
4 4 5 6 7
5 5 6 7 8
Then you can use the which function and the - operator in column indexation :
R> df[ , -which(names(df) %in% c("z","u"))]
x y
1 1...
Python creating a dictionary of lists
...
286
You can use defaultdict:
>>> from collections import defaultdict
>>> d = de...
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Why does 2 mod 4 = 2?
...
152
Mod just means you take the remainder after performing the division. Since 4 goes into 2 zero ti...
Removing duplicates from a list of lists
...
>>> k = [[1, 2], [4], [5, 6, 2], [1, 2], [3], [4]]
>>> import itertools
>>> k.sort()
>>> list(k for k,_ in itertools.groupby(k))
[[1, 2], [3], [4], [5, 6, 2]]
itertools often offers the fastest and most powerf...
Extract elements of list at odd positions
...
232
Solution
Yes, you can:
l = L[1::2]
And this is all. The result will contain the elements p...
Filter rows which contain a certain string
...
263
The answer to the question was already posted by the @latemail in the comments above. You can ...
Concatenating two one-dimensional NumPy arrays
...separate arguments.
From the NumPy documentation:
numpy.concatenate((a1, a2, ...), axis=0)
Join a sequence of arrays together.
It was trying to interpret your b as the axis parameter, which is why it complained it couldn't convert it into a scalar.
...