Errata

It seems that "65%" is not correct in the following sentence and must be changed to "79166.67/(61500+48000)=72.3%"!

Data scientists with more than five years experience
earn 65% more than data scientists with little or no experience!

The text in the ebook and printed book says:

sorted(num_friend_by_id, key=lambda...

but lambda is deprecated and does not work. The specific error message is:

"tuple unpacking is not supported in Python 3"

sorted(num_friends_by_id,
key=lambda (user_id, num_friends): num_friends,
reverse=True)
# code provided in book (above) does not work in Python3 due to invalid syntax

# this works
sorted(num_friends_by_id,
key=lambda num_friends: num_friends[1],
reverse=True)

The line of code in the printed and pdf version reads:

print friends_of_friend_ids(users[3])

it should have an extra left parenthesis, as follows:

print (friends_of_friend_ids(users[3])

Note this is correct on the github page:

https://github.com/joelgrus/data-science-from-scratch/blob/master/code-python3/introduction.py

Both the printed and ePub version have three lines in the middle of the page that start:

print [friend["id"] for friend in users[0]["friends"]]

The other two print lines are analogous.

The print command is missing parentheses and does not run on my system (Python 3.6, up to date). Adding parentheses allows the lines to run correctly:

print([friend["id"] for friend in users[0]["friends"])

The line in question is:

for tenure_bucket, salaries in salary_by_tenure_bucket.iteritems()

That generates an error message (Python 3.6.0, PyCharm 2016.3.3):

AttributeError: 'collections.defaultdict' object has no attribute 'iteritems'

A line that runs is:

for tenure_bucket, salaries in salary_by_tenure_bucket.items()

for the line

import re as regex

Python reports that regex is an alternative regular expression module, to replace re. In other words, re is now out of date.

See here for more details:

https://bitbucket.org/mrabarnett/mrab-regex

the text claims that this bit of code:
s = some_function_that_returns_a_string()
if s:
first_char = s[0]
else:
first_char = ""

is equivalent, due to truthiness, to this:
first_char = s and s[0]

This is not accurate.

As an example, assume either s = None
The result of the above if statement will be first_char equal ""
The result of first_char = s and s[0] will be first_char equal to None

The code says:

"# label x-axis with movie names at bar centers

plt.xticks( [ i + 0.5 for i, _ in enumerate(movies) ], movies)

plt.show()"

The 0.5 in plt.xticks should be replaced with the value 0.1 so that the movie names are at the bar centers. Thus the code should be:

plt.xticks( [ i + 0.1 for i, _ in enumerate(movies) ], movies)

def vector_mean(vectors):
"""compute the vector whose ith element is the mean of the
ith elements of the input vectors"""
n = len(vectors)
return scalar_multiply(1/n, vector_sum(vectors))


When you run the vector_mean function the result is always a vector full of zeros unless the list of vectors passed into the function only contains one vector. The scalar_multiply function has 1/n passed into it, but this is rounded to 0 when dividing 1 by any integer greater than 1.

This is corrected by changing the 4th line of code to:

n = float(len(vectors))

Rejection range is incorrent.

"... rejects H0 when X is between 526 and 531 ..."

It should be

"... rejects H0 when X is larger than 526 ..."

There i see below sentence:

And changing one of our data points by a small amount e might increase the median by e, by some number less than e, or not at all (depending on the rest of the data).

I'm confused. Changing a value might change the median by e?
I think the median does not change until number changing happened in a way that sorted array of number change the data before and after the median.