why should I make a copy of a data frame in pandas

This expands on Paul’s answer. In Pandas, indexing a DataFrame returns a reference to the initial DataFrame. Thus, changing the subset will change the initial DataFrame. Thus, you’d want to use the copy if you want to make sure the initial DataFrame shouldn’t change. Consider the following code: You’ll get: In contrast, the following leaves …

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Adding new column to existing DataFrame in Python pandas

Edit 2017 As indicated in the comments and by @Alexander, currently the best method to add the values of a Series as a new column of a DataFrame could be using assign: Edit 2015Some reported getting the SettingWithCopyWarning with this code.However, the code still runs perfectly with the current pandas version 0.16.1. The SettingWithCopyWarning aims to inform of a possibly …

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How to deal with SettingWithCopyWarning in Pandas

The SettingWithCopyWarning was created to flag potentially confusing “chained” assignments, such as the following, which does not always work as expected, particularly when the first selection returns a copy. [see GH5390 and GH5597 for background discussion.] The warning offers a suggestion to rewrite as follows: However, this doesn’t fit your usage, which is equivalent to: While it’s clear that you don’t care …

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How to deal with SettingWithCopyWarning in Pandas

The SettingWithCopyWarning was created to flag potentially confusing “chained” assignments, such as the following, which does not always work as expected, particularly when the first selection returns a copy. [see GH5390 and GH5597 for background discussion.] The warning offers a suggestion to rewrite as follows: However, this doesn’t fit your usage, which is equivalent to: While it’s clear that you don’t care …

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