NumPy & SciPy

Question 1

create three-dimensional array of floats

Answer 1

import numpy
x = y = z = 5
zeros((x, y, z), np.float)

Question 2

get array/matrix dimensions

Answer 2

a.shape

Question 3

get array/matrix datatype

Answer 3

a.dtype

Question 4

given an array a, make a new array of same dimension and data type

Answer 4

x = zeros(a.shape, a.dtype)

Question 5

create a list of uniformly spaced coordinates

Answer 5

linspace(start, end, steps)

Question 6

construct array from list

Answer 6

array(list)

Question 7

construct 2D-array from two lists

Answer 7

array([x, y])

Question 8

from array to list

Answer 8

a.tolist()

Question 9

convert to array

Answer 9

asarray(list)

Question 10

change array dimensions

Answer 10

a.shape = (3, 2)
a = a.reshape(3, 2)

Question 11

get number of elements in array

Answer 11

a.size

Question 12

set a[2] and a[3] equal to 5

Answer 12

a[2:4] = 5

Question 13

set last element equal to first

Answer 13

a[-1] = a[0]

Question 14

set all elements of array equal to 0

Answer 14

a[:] = 0
a[:, :] = 0
a.fill(0)

Question 15

print column k

Answer 15

print a[:, k]

Question 16

print row l

Answer 16

print a[l, :]

Question 17

a[:, ::2]

Answer 17

returns first and even indexed elements in all rows

Question 18

a[:, 2::2]

Answer 18

returns even indexed elements in all rows

Question 19

list[:] is a … of the data

array[:] is a … of the data

Answer 19

copy

reference

Question 20

copy array

Answer 20

b = a.copy()

Question 21

loop over 2D-array

Answer 21

for y in xrange(a.shape[0]):
for x in xrange(a.shape[1]):
print a[y, x]

Question 22

perform 2x + 1 on every element in a

Answer 22

a = 2*a + 1
# this is much faster than element-wise operations

Question 23

power function

Answer 23

x**2

Question 24

exponential function

Answer 24

exp(a)

Question 25

square root function

Answer 25

sqrt(a)

Question 26

get mean, variance and standard deviation of array a

Answer 26

a. mean(), mean(a)
a. var(), var(a)
a. std(), std(a)

Question 27

covariance

Answer 27

cov(x, y)

Question 28

change type of array/matrix

Answer 28

a.astype(int)

Question 29

module for curve plotting

Answer 29

matplotlib