Variables¶

Learning objectives

use a variable

For teachers

Teaching goals are:

Learners have practiced using a variable

Lesson plan:

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

Overview¶

Sometimes we need AWK to remember things, for example, when summing values

Exercises¶

See the exercise procedure here.

Exercise 1: confirming things are true¶

Learning objectives

experience variables

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.

Sum¶

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

awk '{ sum = sum + $2 } END { print sum }' coins.txt

In English, this is: 'For every line, add the value of the second column to the variable called sum. In the end, print the value of sum.

Confirm that this is true.

Get the maximum¶

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

awk '$2 > max { max = $2 } END { print max }' coins.txt

In English, this is: 'For every line, if the value in the second column is bigger than the value of max, set max to the value in the second column. In the end, print the value of max.

Confirm that this is true.

What is the assumption about the values in the second column?

The assumption about the values in the second column is that zero is the lowest possible value, as the initial value of max is zero.

If, for example, all the values in the second column are negative, max will be zero.

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.

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
show the number of columns in the dataset
show the lowest price of all the diamonds
show the average price of all the diamonds
show the average price of all the diamonds with an ideal cut
show the total weight of all diamonds combined in kilos, 1 carat is 0.0002 kilo
show the prices of all the diamonds together, in Swedish kroner. Assume 1 US dollar is 10.47 Swedish kroner