Python NumPy Exercises#
Question: 1. Import the numpy package under the name np and print the numpy version and the configuration (★☆☆)
Hint: import … as and np.__version__, np.show_config)
# Write your code here
Question: 2. Convert a list of numeric value into a one-dimensional NumPy array (★☆☆)
💡 hint: numpy.array
# Write your code here
Question: 3. Create a null vector of size 9 (★☆☆)
💡 hint: np.zeros
# Write your code here
#Question: 4. How to find the memory size of any array (★☆☆)
💡 hint: size, itemsize
# Write your code here
Question: 5. How to get the documentation of the numpy add function from the command line? (★☆☆)
💡hint: np.info
# Write your code here
Question: 6. Create a null vector of size 12 but the sixth value which is 1 (★☆☆)
💡hint: array[12]
# Write your code here
Question: 7. Create a vector with values ranging from 20 to 59 (★☆☆)
💡hint: arange
# Write your code here
#Question: 8. Reverse a vector (first element becomes last) (★☆☆)
💡hint: array[::-1]
# Write your code here
Question: 9. Create a 3x3 matrix with values ranging from 12 to 20 (★☆☆)
💡hint: reshape
# Write your code here
Question: 10. Find indices of non-zero elements from [3,7,0,0,9,0] (★☆☆)
💡hint: np.nonzero
# Write your code here
Question: 11. Create a 4x4 identity matrix (★☆☆)
💡hint: np.eye
# Write your code here
Question: 12. Create a 2x2x2 array with random values (★☆☆)
💡hint: np.random.random
# Write your code here
Question: 13. Create a 9x9 array with random values and find the minimum and maximum values (★☆☆)
💡hint: min, max
# Write your code here
Question: 6# 6# 14. Create a random vector of size 20 and find the mean value (★☆☆)
💡hint: mean
# Write your code here
Question: 15. Create a 2d array with 1 on the border and 0 inside (★☆☆)
💡hint: array[1:-1, 1:-1]
# Write your code here
Question: 16. How to add a border (filled with 0’s) around an existing array? (★☆☆)
💡hint: np.pad
# Write your code here
Question: 17. What is the result of the following expression? (★☆☆)
0 * np.nan
np.nan == np.nan
np.inf > np.nan
np.nan - np.nan
np.nan in set([np.nan])
0.7 == 7 * 0.1
💡hint: NaN = not a number, inf = infinity
# Write your code here
Question: 18. Create a 6x6 matrix with values 1,2,3,4 just below the diagonal (★☆☆)
💡hint: np.diag
# Write your code here
Question: 19. Create a 6x6 matrix and fill it with a checkerboard pattern (★☆☆)
💡hint: array[::2]
# Write your code here
Question: 20. Consider a (8,9,10) shape array, what is the index (x,y,z) of the 100th element? (★☆☆)
💡hint: np.unravel_index
# Write your code here
Question: 21. Create a checkerboard 8x8 matrix using the tile function (★☆☆)
💡hint: np.tile
# Write your code here
Question: 22. Normalize a 6x6 random matrix (★☆☆)
💡hint: (x -mean)/std
# Write your code here
Question: 23. find the number of elements of an array, length of one array element in bytes and total bytes consumed by the elements. (★☆☆)
# Write your code here
Question: 24. Multiply a 6x3 matrix by a 3x4 matrix (real matrix product) (★☆☆)
💡hint: np.dot or np.ones
# Write your code here
Question: 25. Given a 1D array, negate all elements which are between 3 and 8, in place. (★☆☆)
💡hint: >, <
# Write your code here
Question: 26. What is the output of the following script? (★☆☆)
print(sum(range(5),-1))
from numpy import *
print(sum(range(5),-1))
# Write your code here
Question: 27. Write a Python program compare two arrays using numpy (★☆☆)
Array a: [1 2]
Array b: [4 5]
a > b
[False False]
a >= b
[False False]
a < b
[ True True]
a <= b
[ True True]
# Write your code here
Question: 28. What are the result of the following expressions? (★☆☆)
np.array(0) / np.array(0)
np.array(0) // np.array(0)
np.array([np.nan]).astype(int).astype(float)
Consider an integer vector a
a**a
a << a >> 2
a <- a
1j*a
a/1/1
a<a>a
# Write your code here
Question: 29. How to round away from zero a float array ? (★☆☆)
💡hint: np.uniform, np.copysign, np.ceil, np.abs, np.where
# Write your code here
Question: 30. How to find common values between two arrays? (★☆☆)
💡hint: np.intersect1d
# Write your code here
Question: 31. How to ignore all numpy warnings (not recommended)? (★☆☆)
💡hint: np.seterr, np.errstate
# Write your code here
Question: 32. Is the following expressions true? (★☆☆)
np.sqrt(-1) == np.emath.sqrt(-1)
💡hint: imaginary number
# Write your code here
Question: 33. How to get the dates of yesterday, today and tomorrow? (★☆☆)
💡hint: np.datetime64, np.timedelta64
# Write your code here
Question: 34. How to get all the dates corresponding to the month of January 2016? (★★☆)
💡hint: np.arange(dtype=datetime64['D'])
# Write your code here
Question: 35. How to compute ((A+B)*(-A/2)) in place (without copy)? (★★☆)
💡hint: np.add(out=), np.negative(out=), np.multiply(out=), np.divide(out=)
# Write your code here
Question: 36. Extract the integer part of a random array of positive numbers using 4 different methods (★★☆)
💡hint: %, np.floor, astype, np.trunc
# Write your code here
Question: 37. Create a 3x3 matrix with row values ranging from 0 to 2 (★★☆)
💡hint: np.arange
# Write your code here
Question: 38. Consider a generator function that generates 9 integers and use it to build an array (★☆☆)
💡hint: np.fromiter
# Write your code here
Question: 39. Create a vector of size 10 with values ranging from 0 to 1, both excluded (★★☆)
💡hint: np.linspace
# Write your code here
Question: 40. Create a random vector of size 10 and sort it (★★☆)
💡hint: sort
# Write your code here
Question: 41. How to sum a small array faster than np.sum? (★★☆)
💡hint: np.add.reduce
# Write your code here
Question: 42. Consider two random array A and B, check if they are equal (★★☆)
💡hint: np.allclose, np.array_equal
# Write your code here
Question: 43. Make an array immutable (read-only) (★★☆)
💡hint: flags.writeable
# Write your code here
Question: 44. Consider a random 5x2 matrix representing cartesian coordinates, convert them to polar coordinates (★★☆)
💡hint: np.sqrt, np.arctan2
# Write your code here
Question: 45. Create random vector of size 5 and replace the maximum value by 0 (★★☆)
💡hint: argmax
# Write your code here
Question: 46. Create a structured array with x and y coordinates covering the [0,1]x[0,1] area (★★☆)
💡hint: np.meshgrid
# Write your code here
Question: 47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj)) (★★☆)
💡hint: np.subtract.outer
# Write your code here
Question: 48. Print the minimum and maximum representable value for each numpy scalar type (★★☆)
💡hint: np.iinfo, np.finfo, eps
# Write your code here
Question: 49. How to print all the values of an array? (★★☆)
💡hint: np.set_printoptions
# Write your code here
Question: 50. How to find the closest value (to a given scalar) in a vector? (★★☆)
💡hint: argmin
# Write your code here
Question: 51. Create a structured array representing a position (x,y) and a color (r,g,b) (★★☆)
💡hint: dtype
# Write your code here
Question: 52. Consider a random vector with shape (100,2) representing coordinates, find point by point distances (★★☆)
💡hint: np.atleast_2d, T, np.sqrt
# Write your code here
Question: 53. How to convert a float (32 bits) array into an integer (32 bits) in place?
💡hint: view and [:] =
# Write your code here
Question: 54. How to read the following file? (★★☆)
1, 2, 3, 4, 5
6, , , 7, 8
, , 9,10,11
💡hint: np.genfromtxt
# Write your code here
Question: 55. What is the equivalent of enumerate for numpy arrays? (★★☆)
💡hint: np.ndenumerate, np.ndindex
# Write your code here
Question: 56. Generate a generic 2D Gaussian-like array (★★☆)
💡hint: np.meshgrid, np.exp
# Write your code here
Question: 57. How to randomly place e elements in a 2D array? (★★☆)
💡hint: np.put, np.random.choice
# Write your code here
Question: 58. Subtract the mean of each row of a matrix (★★☆)
💡hint: mean(axis=,keepdims=)
# Write your code here
Question: 59. How to sort an array by the nth column? (★★☆)
💡hint: argsort
# Write your code here
Question: 60. How to tell if a given 2D array has null columns? (★★☆)
💡hint: any, ~
# Write your code here
Question: 61. Find the nearest value from a given value in an array (★★☆)
💡hint: np.abs, argmin, flat
# Write your code here
Question: 62. Considering two arrays with shape (1,3) and (3,1), how to compute their sum using an iterator? (★★☆) `💡
# Write your code here
Question: 63. Create an array class that has a name attribute (★★☆)
💡hint: class method
# Write your code here
Question: 64. Consider a given vector, how to add 1 to each element indexed by a second vector (be careful with repeated indices)? (★★★)
💡hint: np.bincount | np.add.at
# Write your code here
Question: 65. How to accumulate elements of a vector (X) to an array (F) based on an index list (I)? (★★★)
💡hint: np.bincount
# Write your code here
Question: 66. Considering a (w,h,3) image of (dtype=ubyte), compute the number of unique colors (★★☆)
💡hint: np.unique
# Write your code here
Question: 67. Considering a four dimensions array, how to get sum over the last two axis at once? (★★★)
💡hint: sum(axis=(-2,-1))
# Write your code here
Question: 68. Considering a one-dimensional vector D, how to compute means of subsets of D using a vector S of same size describing subset indices? (★★★)
💡hint: np.bincount
# Write your code here
Question: 69. How to get the diagonal of a dot product? (★★★)
💡hint: np.diag
# Write your code here
Question: 70. Consider the vector [1, 2, 3, 4, 5], how to build a new vector with 3 consecutive zeros interleaved between each value? (★★★)
💡hint: array[::4]
# Write your code here
Question: 71. Consider an array of dimension (5,5,3), how to mulitply it by an array with dimensions (5,5)? (★★★)
💡hint: array[:, :, None]
# Write your code here
Question: 72. How to swap two rows of an array? (★★★)
💡hint: array[[]] = array[[]]
# Write your code here
Question: 73. Consider a set of 10 triplets describing 10 triangles (with shared vertices), find the set of unique line segments composing all the triangles (★★★)
💡hint: repeat, np.roll, np.sort, view, np.unique
# Write your code here
Question: 74. Given a sorted array C that corresponds to a bincount, how to produce an array A such that np.bincount(A) == C? (★★★)
💡hint: np.repeat
# Write your code here
Question: 75. How to compute averages using a sliding window over an array? (★★★)
💡hint: np.cumsum
# Write your code here
Question: 76. Consider a one-dimensional array Z, build a two-dimensional array whose first row is (Z[0],Z[1],Z[2]) and each subsequent row is shifted by 1 (last row should be (Z[-3],Z[-2],Z[-1]) (★★★)
💡hint: from numpy.lib import stride_tricks
# Write your code here
Question: 77. How to negate a boolean, or to change the sign of a float inplace? (★★★)
💡hint: np.logical_not, np.negative
# Write your code here
Question: 78. Consider 2 sets of points P0,P1 describing lines (2d) and a point p, how to compute distance from p to each line i (P0[i],P1[i])? (★★★)
# Write your code here
Question: 79. Consider 2 sets of points P0,P1 describing lines (2d) and a set of points P, how to compute distance from each point j (P[j]) to each line i (P0[i],P1[i])? (★★★)
# Write your code here
Question: 80. Consider an arbitrary array, write a function that extract a subpart with a fixed shape and centered on a given element (pad with a fill value when necessary) (★★★)
💡hint: minimum maximum
# Write your code here
Question: 81. Consider an array a = [1,2,3,4,5,6,7,8,9,10,11,12,13,14], how to generate an array b = [[1,2,3,4], [2,3,4,5], [3,4,5,6], …, [11,12,13,14]]? (★★★)
💡hint: stride_tricks.as_strided
# Write your code here
Question: 82. Compute a matrix rank (★★★)
💡hint: np.linalg.svd
# Write your code here
Question: 83. How to find the most frequent value in an array?
💡hint: np.bincount, argmax
# Write your code here
Question: 84. Extract all the contiguous 3x3 blocks from a random 10x10 matrix (★★★)
💡hint: stride_tricks.as_strided
# Write your code here
Question: 85. Create a 2D array subclass such that a[i,j] == a[j,i] (★★★)
💡hint: class method
# Write your code here
Question: 86. Consider a set of p matrices wich shape (n,n) and a set of p vectors with shape (n,1). How to compute the sum of of the p matrix products at once? (result has shape (n,1)) (★★★)
💡hint: np.tensordot
# Write your code here
Question: 87. Consider a 16x16 array, how to get the block-sum (block size is 4x4)? (★★★)
💡hint: np.add.reduceat
# Write your code here
Question: 88. How to implement the Game of Life using numpy arrays? (★★★)
# Write your code here
Question: 89. How to get the n largest values of an array (★★★)
💡hint: np.argsort | np.argpartition
# Write your code here
Question: 90. Given an arbitrary number of vectors, build the cartesian product (every combinations of every item) (★★★)
💡hint: np.indices
# Write your code here
Question: 91. How to create a record array from a regular array? (★★★)
💡hint: np.core.records.fromarrays
# Write your code here
Question: 92. Consider a large vector A, compute A to the power of 3 using 3 different methods (★★★)
💡hint: np.power, *, np.einsum
# Write your code here
Question: 93. Consider two arrays A and B of shape (8,3) and (2,2). How to find rows of A that contain elements of each row of B regardless of the order of the elements in B? (★★★)
💡hint: np.where
# Write your code here
Question: 94. Considering a 10x3 matrix, extract rows with unequal values (e.g. [2,2,3]) (★★★)
# Write your code here
Question: 95. Convert a vector of ints into a matrix binary representation (★★★)
💡hint: np.unpackbits
# Write your code here
Question: 96. Given a two dimensional array, how to extract unique rows? (★★★)
💡hint: np.ascontiguousarray | np.unique
# Write your code here
Question: 97. Considering 2 vectors A & B, write the einsum equivalent of inner, outer, sum, and mul function (★★★)
💡hint: np.einsum
# Write your code here
Question: 98. Considering a path described by two vectors (X,Y), how to sample it using equidistant samples (★★★)?
💡hint: np.cumsum, np.interp
# Write your code here
Question: 99. Given an integer n and a 2D array X, select from X the rows which can be interpreted as draws from a multinomial distribution with n degrees, i.e., the rows which only contain integers and which sum to n. (★★★)
💡hint: np.logical_and.reduce, np.mod
# Write your code here
Question: 100. Compute bootstrapped 95% confidence intervals for the mean of a 1D array X (i.e., resample the elements of an array with replacement N times, compute the mean of each sample, and then compute percentiles over the means). (★★★)
💡hint: np.percentile
# Write your code here