numpy 100题练习 Day4

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https://github.com/rougier/numpy-100

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# Suicide mode on
defaults = np.seterr(all="ignore")
Z = np.ones(1) / 0

# Back to sanity
_ = np.seterr(**defaults)

An equivalent way, with a context manager:

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with np.errstate(divide='ignore'):
    Z = np.ones(1) / 0

Is the following expressions true?

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np.sqrt(-1) == np.emath.sqrt(-1)

How to get the dates of yesterday, today and tomorrow?

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yesterday = np.datetime64('today', 'D') - np.timedelta64(1, 'D')
today     = np.datetime64('today', 'D')
tomorrow  = np.datetime64('today', 'D') + np.timedelta64(1, 'D')

How to get all the dates corresponding to the month of July 2016?

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Z = np.arange('2016-07', '2016-08', dtype='datetime64[D]')
print(Z)

How to compute ((A+B)*(-A/2)) in place (without copy)?

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A = np.ones(3)*1
B = np.ones(3)*2
C = np.ones(3)*3
np.add(A,B,out=B)
np.divide(A,2,out=A)
np.negative(A,out=A)
np.multiply(A,B,out=A)

Extract the integer part of a random array using 5 different methods

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Z = np.random.uniform(0,10,10)

print (Z - Z%1)
print (np.floor(Z))
print (np.ceil(Z)-1)
print (Z.astype(int))
print (np.trunc(Z))

Create a 5x5 matrix with row values ranging from 0 to 4

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Z = np.zeros((5,5))
Z += np.arange(5)
print(Z)

Consider a generator function that generates 10 integers and use it to build an array

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def generate():
    for x in range(10):
        yield x
Z = np.fromiter(generate(),dtype=float,count=-1)
print(Z)

Create a vector of size 10 with values ranging from 0 to 1, both excluded

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Z = np.linspace(0,1,11,endpoint=False)[1:]
print(Z)

Create a random vector of size 10 and sort it

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Z = np.random.random(10)
Z.sort()
print(Z)