unexplained items in lesson3

[jrmcgarvey]

In the examples given in lesson3 for creation of series and dataframes, sometimes the indexes are given, and sometimes they aren't. The lesson should explain how the indexes are created if they aren't specified, and how to specify an index when creating a dataframe.

Lesson 3 does not explain vector operations on a series, although the assignment requires this.

Lesson 3 does not explain how to add a column to a dataframe, although the assignment requires this.

Lesson 3 does not explain concat() of dataframes or series, although the assignment requires this.

The lesson should explain what happens when there is a concat() of dataframes and the column names are not the same. The lesson should explain how to reset the index after concat. The lesson should explain about the use of axis= with concat.

Lesson 3 does not explain about column labels, or that a column in a dataframe is a series.

Lesson 3 does not explain what a correlation is. The assignment uses the corr() method, and students can call it, but they won't know what the results mean.

[jrmcgarvey]

More on operations on a series: we should give examples like, for series s, statements like s += 2. And we should give an example of s.map(). Finally, we might give an example of a numpy vectorized operation, like s = numpy.sqrt(s). Maybe s.apply()? Perhaps apply() is an advanced topic.