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devel / comp.lang.python / Re: double bracket integer index in pandas; Is this a legal syntax

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o double bracket integer index in pandas; Is this a legal syntaxCameron Simpson

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Re: double bracket integer index in pandas; Is this a legal syntax

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From: cs@cskk.id.au (Cameron Simpson)
Newsgroups: comp.lang.python
Subject: Re: double bracket integer index in pandas; Is this a legal syntax
Date: Thu, 4 May 2023 12:29:45 +1000
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 by: Cameron Simpson - Thu, 4 May 2023 02:29 UTC

On 03May2023 17:52, Artie Ziff <artie.ziff@gmail.com> wrote:
>The code came from a video course, "Pandas Data Analysis with Python
>Fundamentals" by Daniel Chen.
>
>I am curious why the author may have said this. To avoid attaching
>screenshots, I'll describe this section of the content. Perhaps someone can
>say, "oh that's how it used to work"... haha

Unlikely; Python indices (and by implication Pandas indices) have
counted from 0 since forever. I suspect just a typo/braino.

>D.CHEN:
>"You can also subset the columns by number. If we wanted to get the first
>column from our data set, we would use zero":
>
>df = pandas.read_csv('./data/gapminder.tsv', sep='\t')
>>>> subset = df[[0]]
>>>> print(subset.head())
> country
>0 Afghanistan
>1 Afghanistan
>2 Afghanistan
>3 Afghanistan
>4 Afghanistan
>
>Data for the course:
>https://github.com/chendaniely/pandas_for_everyone.git
>
>"df[[0]]" is being described to the course student as selecting the first
>column of data. :-)

Well, I would say it makes a new dataframe with just the first column.

So:

df[ 0 ] # spaces for clarity

would (probably, need to check) return the Series for the first column.
versus:

df[ [0] ] # spaces for clarity

makes a new dataframe with only the first column.

A dataframe can be thought of as an array of Series (one per column).

Cheers,
Cameron Simpson <cs@cskk.id.au>

devel / comp.lang.python / Re: double bracket integer index in pandas; Is this a legal syntax

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