On 9/25/17 12:44 PM, john polo wrote:
Python List,
I am trying to make practice data for plotting purposes. I am using
Python 3.6. The instructions I have are
import matplotlib.pyplot as plt
import math
import numpy as np
t = np.arange(0, 2.5, 0.1)
y1 = map(math.sin, math.pi*t)
plt.plot(t,y1)
However, at this point, I get a TypeError that says
object of type 'map' has no len()
In [6]: t
Out[6]:
array([ 0. , 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1. ,
1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2. , 2.1,
2.2, 2.3, 2.4])
In [7]: y1
Out[7]: <map at 0x6927128>
In [8]: math.pi*t
Out[8]:
array([ 0. , 0.31415927, 0.62831853, 0.9424778 , 1.25663706,
1.57079633, 1.88495559, 2.19911486, 2.51327412, 2.82743339,
3.14159265, 3.45575192, 3.76991118, 4.08407045, 4.39822972,
4.71238898, 5.02654825, 5.34070751, 5.65486678, 5.96902604,
6.28318531, 6.59734457, 6.91150384, 7.2256631 , 7.53982237])
At the start of creating y1, it appears there is an array to iterate
through for the math.sin function used in map(), but y1 doesn't appear
to be saving any values. I expected y1 to hold a math.sin() output for
each item in math.pi*t, but it appears to be empty. Am I
misunderstanding map()? Is there something else I should be doing
instead to populate y1?
In Python 2, map() produced a list. In Python 3, it returns a lazy
iterator instead. You can run the iterator with list():
y1 = list(map(math.sin, math.pi*t))
--Ned.
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