numpy-100/questsions_dict.py

qha = {
    "q1": "1. Import the numpy package under the name `np` (★☆☆)",
    "h1": "hint: import … as ",
    "a1":
"""
import numpy as np
""",

}
# ####
#
# (**hint**: import … as …)
#
#
#
# #### 2. Print the numpy version and the configuration (★☆☆)
#
# (**hint**: np.\_\_version\_\_, np.show\_config)
#
#
#
# #### 3. Create a null vector of size 10 (★☆☆)
#
# (**hint**: np.zeros)
#
#
#
# #### 4.  How to find the memory size of any array (★☆☆)
#
# (**hint**: size, itemsize)
#
#
#
# #### 5.  How to get the documentation of the numpy add function from the command line? (★☆☆)
#
# (**hint**: np.info)
#
#
#
# #### 6.  Create a null vector of size 10 but the fifth value which is 1 (★☆☆)
#
# (**hint**: array\[4\])
#
#
#
# #### 7.  Create a vector with values ranging from 10 to 49 (★☆☆)
#
# (**hint**: np.arange)
#
#
#
# #### 8.  Reverse a vector (first element becomes last) (★☆☆)
#
# (**hint**: array\[::-1\])
#
#
#
# #### 9.  Create a 3x3 matrix with values ranging from 0 to 8 (★☆☆)
#
# (**hint**: reshape)
#
#
#
# #### 10. Find indices of non-zero elements from \[1,2,0,0,4,0\] (★☆☆)
#
# (**hint**: np.nonzero)
#
#
#
# #### 11. Create a 3x3 identity matrix (★☆☆)
#
# (**hint**: np.eye)
#
#
#
# #### 12. Create a 3x3x3 array with random values (★☆☆)
#
# (**hint**: np.random.random)
#
#
#
# #### 13. Create a 10x10 array with random values and find the minimum and maximum values (★☆☆)
#
# (**hint**: min, max)
#
#
#
# #### 14. Create a random vector of size 30 and find the mean value (★☆☆)
#
# (**hint**: mean)
#
#
#
# #### 15. Create a 2d array with 1 on the border and 0 inside (★☆☆)
#
# (**hint**: array\[1:-1, 1:-1\])
#
#
#
# #### 16. How to add a border (filled with 0's) around an existing array? (★☆☆)
#
# (**hint**: np.pad)
#
#
#
# #### 17. What is the result of the following expression? (★☆☆)
#
# (**hint**: NaN = not a number, inf = infinity)
#
#
# ```python
# 0 * np.nan
# np.nan == np.nan
# np.inf > np.nan
# np.nan - np.nan
# np.nan in set([np.nan])
# 0.3 == 3 * 0.1
# ```
#
# #### 18. Create a 5x5 matrix with values 1,2,3,4 just below the diagonal (★☆☆)
#
# (**hint**: np.diag)
#
#
#
# #### 19. Create a 8x8 matrix and fill it with a checkerboard pattern (★☆☆)
#
# (**hint**: array\[::2\])
#
#
#
# #### 20. Consider a (6,7,8) shape array, what is the index (x,y,z) of the 100th element?
#
# (**hint**: np.unravel\_index)
#
#
#
# #### 21. Create a checkerboard 8x8 matrix using the tile function (★☆☆)
#
# (**hint**: np.tile)
#
#
#
# #### 22. Normalize a 5x5 random matrix (★☆☆)
#
# (**hint**: (x - mean) / std)
#
#
#
# #### 23. Create a custom dtype that describes a color as four unsigned bytes (RGBA) (★☆☆)
#
# (**hint**: np.dtype)
#
#
#
# #### 24. Multiply a 5x3 matrix by a 3x2 matrix (real matrix product) (★☆☆)
#
# (**hint**: np.dot | @)
#
#
#
# #### 25. Given a 1D array, negate all elements which are between 3 and 8, in place. (★☆☆)
#
# (**hint**: >, <=)
#
#
#
# #### 26. What is the output of the following script? (★☆☆)
#
# (**hint**: np.sum)
#
#
# ```python
# # Author: Jake VanderPlas
#
# print(sum(range(5),-1))
# from numpy import *
# print(sum(range(5),-1))
# ```
#
# #### 27. Consider an integer vector Z, which of these expressions are legal? (★☆☆)
#
#
# ```python
# Z**Z
# 2 << Z >> 2
# Z <- Z
# 1j*Z
# Z/1/1
# Z<Z>Z
# ```
#
# #### 28. What are the result of the following expressions?
#
#
# ```python
# np.array(0) / np.array(0)
# np.array(0) // np.array(0)
# np.array([np.nan]).astype(int).astype(float)
# ```
#
# #### 29. How to round away from zero a float array ? (★☆☆)
#
# (**hint**: np.uniform, np.copysign, np.ceil, np.abs)
#
#
#
# #### 30. How to find common values between two arrays? (★☆☆)
#
# (**hint**: np.intersect1d)
#
#
#
# #### 31. How to ignore all numpy warnings (not recommended)? (★☆☆)
#
# (**hint**: np.seterr, np.errstate)
#
#
#
# #### 32. Is the following expressions true? (★☆☆)
#
# (**hint**: imaginary number)
#
#
# ```python
# np.sqrt(-1) == np.emath.sqrt(-1)
# ```
#
# #### 33. How to get the dates of yesterday, today and tomorrow? (★☆☆)
#
# (**hint**: np.datetime64, np.timedelta64)
#
#
#
# #### 34. How to get all the dates corresponding to the month of July 2016? (★★☆)
#
# (**hint**: np.arange(dtype=datetime64\['D'\]))
#
#
#
# #### 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=))
#
#
#
# #### 36. Extract the integer part of a random array using 5 different methods (★★☆)
#
# (**hint**: %, np.floor, np.ceil, astype, np.trunc)
#
#
#
# #### 37. Create a 5x5 matrix with row values ranging from 0 to 4 (★★☆)
#
# (**hint**: np.arange)
#
#
#
# #### 38. Consider a generator function that generates 10 integers and use it to build an array (★☆☆)
#
# (**hint**: np.fromiter)
#
#
#
# #### 39. Create a vector of size 10 with values ranging from 0 to 1, both excluded (★★☆)
#
# (**hint**: np.linspace)
#
#
#
# #### 40. Create a random vector of size 10 and sort it (★★☆)
#
# (**hint**: sort)
#
#
#
# #### 41. How to sum a small array faster than np.sum? (★★☆)
#
# (**hint**: np.add.reduce)
#
#
#
# #### 42. Consider two random array A and B, check if they are equal (★★☆)
#
# (**hint**: np.allclose, np.array\_equal)
#
#
#
# #### 43. Make an array immutable (read-only) (★★☆)
#
# (**hint**: flags.writeable)
#
#
#
# #### 44. Consider a random 10x2 matrix representing cartesian coordinates, convert them to polar coordinates (★★☆)
#
# (**hint**: np.sqrt, np.arctan2)
#
#
#
# #### 45. Create random vector of size 10 and replace the maximum value by 0 (★★☆)
#
# (**hint**: argmax)
#
#
#
# #### 46. Create a structured array with `x` and `y` coordinates covering the \[0,1\]x\[0,1\] area (★★☆)
#
# (**hint**: np.meshgrid)
#
#
#
# ####  47. Given two arrays, X and Y, construct the Cauchy matrix C (Cij =1/(xi - yj))
#
# #####  (hint: np.subtract.outer)
#
#
#
# #### 48. Print the minimum and maximum representable value for each numpy scalar type (★★☆)
#
# (**hint**: np.iinfo, np.finfo, eps)
#
#
#
# #### 49. How to print all the values of an array? (★★☆)
#
# (**hint**: np.set\_printoptions)
#
#
#
# #### 50. How to find the closest value (to a given scalar) in a vector? (★★☆)
#
# (**hint**: argmin)
#
#
#
# #### 51. Create a structured array representing a position (x,y) and a color (r,g,b) (★★☆)
#
# (**hint**: dtype)
#
#
#
# #### 52. Consider a random vector with shape (100,2) representing coordinates, find point by point distances (★★☆)
#
# (**hint**: np.atleast\_2d, T, np.sqrt)
#
#
#
# #### 53. How to convert a float (32 bits) array into an integer (32 bits) in place?
#
# (**hint**: astype(copy=False))
#
#
#
# #### 54. How to read the following file? (★★☆)
#
# (**hint**: np.genfromtxt)
#
#
# ```
# 1, 2, 3, 4, 5
# 6,  ,  , 7, 8
#  ,  , 9,10,11
# ```
#
# #### 55. What is the equivalent of enumerate for numpy arrays? (★★☆)
#
# (**hint**: np.ndenumerate, np.ndindex)
#
#
#
# #### 56. Generate a generic 2D Gaussian-like array (★★☆)
#
# (**hint**: np.meshgrid, np.exp)
#
#
#
# #### 57. How to randomly place p elements in a 2D array? (★★☆)
#
# (**hint**: np.put, np.random.choice)
#
#
#
# #### 58. Subtract the mean of each row of a matrix (★★☆)
#
# (**hint**: mean(axis=,keepdims=))
#
#
#
# #### 59. How to sort an array by the nth column? (★★☆)
#
# (**hint**: argsort)
#
#
#
# #### 60. How to tell if a given 2D array has null columns? (★★☆)
#
# (**hint**: any, ~)
#
#
#
# #### 61. Find the nearest value from a given value in an array (★★☆)
#
# (**hint**: np.abs, argmin, flat)
#
#
#
# #### 62. Considering two arrays with shape (1,3) and (3,1), how to compute their sum using an iterator? (★★☆)
#
# (**hint**: np.nditer)
#
#
#
# #### 63. Create an array class that has a name attribute (★★☆)
#
# (**hint**: class method)
#
#
#
# #### 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)
#
#
#
# #### 65. How to accumulate elements of a vector (X) to an array (F) based on an index list (I)? (★★★)
#
# (**hint**: np.bincount)
#
#
#
# #### 66. Considering a (w,h,3) image of (dtype=ubyte), compute the number of unique colors (★★★)
#
# (**hint**: np.unique)
#
#
#
# #### 67. Considering a four dimensions array, how to get sum over the last two axis at once? (★★★)
#
# (**hint**: sum(axis=(-2,-1)))
#
#
#
# #### 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)
#
#
#
# #### 69. How to get the diagonal of a dot product? (★★★)
#
# (**hint**: np.diag)
#
#
#
# #### 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\[::4\])
#
#
#
# #### 71. Consider an array of dimension (5,5,3), how to mulitply it by an array with dimensions (5,5)? (★★★)
#
# (**hint**: array\[:, :, None\])
#
#
#
# #### 72. How to swap two rows of an array? (★★★)
#
# (**hint**: array\[\[\]\] = array\[\[\]\])
#
#
#
# #### 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)
#
#
#
# #### 74. Given an array C that is a bincount, how to produce an array A such that np.bincount(A) == C? (★★★)
#
# (**hint**: np.repeat)
#
#
#
# #### 75. How to compute averages using a sliding window over an array? (★★★)
#
# (**hint**: np.cumsum)
#
#
#
# #### 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)
#
#
#
# #### 77. How to negate a boolean, or to change the sign of a float inplace? (★★★)
#
# (**hint**: np.logical_not, np.negative)
#
#
#
# #### 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\[i\])? (★★★)
#
#
#
# #### 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\[i\])? (★★★)
#
#
#
# #### 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)
#
#
#
# #### 81. Consider an array Z = \[1,2,3,4,5,6,7,8,9,10,11,12,13,14\], how to generate an array R = \[\[1,2,3,4\], \[2,3,4,5\], \[3,4,5,6\], ..., \[11,12,13,14\]\]? (★★★)
#
# (**hint**: stride\_tricks.as\_strided)
#
#
#
# #### 82. Compute a matrix rank (★★★)
#
# (**hint**: np.linalg.svd)
#
#
#
# #### 83. How to find the most frequent value in an array?
#
# (**hint**: np.bincount, argmax)
#
#
#
# #### 84. Extract all the contiguous 3x3 blocks from a random 10x10 matrix (★★★)
#
# (**hint**: stride\_tricks.as\_strided)
#
#
#
# #### 85. Create a 2D array subclass such that Z\[i,j\] == Z\[j,i\] (★★★)
#
# (**hint**: class method)
#
#
#
# #### 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)
#
#
#
# #### 87. Consider a 16x16 array, how to get the block-sum (block size is 4x4)? (★★★)
#
# (**hint**: np.add.reduceat)
#
#
#
# #### 88. How to implement the Game of Life using numpy arrays? (★★★)
#
#
#
# #### 89. How to get the n largest values of an array (★★★)
#
# (**hint**: np.argsort | np.argpartition)
#
#
#
# #### 90. Given an arbitrary number of vectors, build the cartesian product (every combinations of every item) (★★★)
#
# (**hint**: np.indices)
#
#
#
# #### 91. How to create a record array from a regular array? (★★★)
#
# (**hint**: np.core.records.fromarrays)
#
#
#
# #### 92. Consider a large vector Z, compute Z to the power of 3 using 3 different methods (★★★)
#
# (**hint**: np.power, \*, np.einsum)
#
#
#
# #### 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)
#
#
#
# #### 94. Considering a 10x3 matrix, extract rows with unequal values (e.g. \[2,2,3\]) (★★★)
#
#
#
# #### 95. Convert a vector of ints into a matrix binary representation (★★★)
#
# (**hint**: np.unpackbits)
#
#
#
# #### 96. Given a two dimensional array, how to extract unique rows? (★★★)
#
# (**hint**: np.ascontiguousarray | np.unique)
#
#
#
# #### 97. Considering 2 vectors A & B, write the einsum equivalent of inner, outer, sum, and mul function (★★★)
#
# (**hint**: np.einsum)
#
#
#
# #### 98. Considering a path described by two vectors (X,Y), how to sample it using equidistant samples (★★★)?
#
# (**hint**: np.cumsum, np.interp)
#
#
#
# #### 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)
#
#
#
# #### 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)
#