print

Learning objectives

• print a line
• print a column of a line
• print the line number
• print the number of columns
• print a multiplied value

For teachers

Teaching goals are:

• Learners can print a line
• Learners can print a column of a line
• Learners can print the line number
• Learners can print the number of columns
• Learners can print a multiplied value

Lesson plan:

• 5 mins: prior knowledge
• 5 mins: presentation
• 15 mins: challenge
• 5 mins: feedback

Overview

AWK is great for printing parts of tabular data.

In this session, we use AWK to print.

Exercises

See the exercise procedure here.

Exercise 1: confirming things are true

Learning objectives

• experience the many printing statements of awk

Download the data

In a terminal, do:

wget https://pmitev.github.io/to-awk-or-not/data/coins.txt

to download a file called coins.txt.

This file is a tab-separated file, with the following columns:

index	description
1	metal
2	weight in ounces
3	data minted
4	country of origin
5	description

print

In a terminal, in the same folder as where the data is downloaded, do:

awk '{ print }' coins.txt

In English, this is: 'For every line, print the whole line'.

Confirm that this is true.

print and $0

In a terminal, in the same folder as where the data is downloaded, do:

awk '{ print $0 }' coins.txt

In English, this is: 'For every line, print the whole line'.

Confirm that this is true.

$1

In a terminal, in the same folder as where the data is downloaded, do:

awk '{ print $1 }' coins.txt

In English, this is: 'For every line, print the first column'.

Confirm that this is true.

Multiple columns

In a terminal, in the same folder as where the data is downloaded, do:

awk '{ print $1 $2 }' coins.txt

In English, this is: 'For every line, print the first column and second column'.

Confirm that this is true.

Multiple columns separated by a space

In a terminal, in the same folder as where the data is downloaded, do:

awk '{ print $1, $2 }' coins.txt

In English, this is: 'For every line, print the first column and second column, separated by a space'.

Confirm that this is true.

NF

In a terminal, in the same folder as where the data is downloaded, do:

awk '{ print NF }' coins.txt

In English, this is: 'For every line, print the number of columns'.

Confirm that this is true.

$NF

In a terminal, in the same folder as where the data is downloaded, do:

awk '{ print $NF }' coins.txt

In English, this is: 'For every line, print the last column'.

Confirm that this is true.

NR

In a terminal, in the same folder as where the data is downloaded, do:

awk '{ print NR }' coins.txt

In English, this is: 'For every line, print that line's number'.

Confirm that this is true.

Convert

The second column shows the weight in ounces. One ounce is 28.349523125 gram.

In a terminal, in the same folder as where the data is downloaded, do:

awk '{ print $2 * 28.349523125 }' coins.txt

In English, this is: 'For every line, show the second column multiplied by 28.349523125'.

Confirm that this is true.

Add text

The second column shows the weight in ounces. One ounce is 28.349523125 gram.

In a terminal, in the same folder as where the data is downloaded, do:

awk '{ print $2 * 28.349523125, "gram" }' coins.txt

In English, this is: 'For every line, show the second column multiplied by 28.349523125 and add the word 'gram' (separated by a whitespace)'.

Confirm that this is true.

Exercise 2: explore data

Download the data

In a terminal, do:

wget https://raw.githubusercontent.com/richelbilderbeek/awk_course/master/data/diamonds_no_header.tsv

to download a file called diamonds_no_header.tsv.

This file is a tab-separated file about diamonds and is part of the ggplot2 R package.

• Raw data
• Data description

The dataset has the following columns:

index	name	description
1	carat	weight of the diamond (0.2--5.01)
2	cut	quality of the cut (Fair, Good, Very Good, Premium, Ideal)
3	color	diamond colour, from D (best) to J (worst)
4	clarity	a measurement of how clear the diamond is (I1 (worst), SI2, SI1, VS2, VS1, VVS2, VVS1, IF (best))
5	depth	total depth percentage = z / mean(x, y) = 2 * z / (x + y) (43--79)
6	table	width of top of diamond relative to widest point (43--95)
7	price	price in US dollars (\(326--\)18,823)
8	x	length in mm (0--10.74)
9	y	width in mm (0--58.9)
10	z	depth in mm (0--31.8)

Explore the data

Using awk only:

• show the number of diamonds in the dataset (in any clumsy way!)
• show the number of columns in the dataset (in any clumsy way!)
• show the prices of the diamonds in US dollars
• show the prices of the diamonds in Swedish kroner, assume 1 US dollar is 10.47 Swedish kroner
• show the weight of the diamonds in kilo, 1 carat is 0.0002 kilo

Answer the question:

• At the start of this session, **two ** ways to print all lines were shown (awk '{ print }' coins.txt and awk '{ print $0 }' coins.txt). Although they do exactly the same thing, why were both ways shown?
• All the AWK commands are put in single quotes. Why would that be? Would double quotes work too?