Adding columns in Python

assign returns a new frame, which is what makes chaining safe.

import pandas as pd

frame = pd.DataFrame({"chars": [420, 380], "seconds": [60.0, 45.0]})

wider = frame.assign(
    cps=lambda f: f["chars"] / f["seconds"],
    wpm=lambda f: (f["cps"] * 60 / 5).round(1),
    fast=lambda f: f["wpm"] > 80,
)

print(wider)
print(list(frame.columns))  # untouched

How it works

1. A plain assignment mutates; assign copies.
2. A lambda inside assign sees the frame as it is being built.
3. Several columns in one call are evaluated in order.

Keywords and builtins used here

• as
• lambda
• list
• print

The run, in numbers

Lines

12

Characters to type

283

Tokens

109

Three-star pace

105 tpm

At the three-star pace of 105 tokens a minute, this run takes about 62 seconds.

Type this snippet

Step 1 of 5 in Deriving columns, step 9 of 26 in pandas.

← Previous Next →