Lhasa - Easy Math

#bash #cut #wc
Type: Do
Description: There's a file /home/admin/scores.txt with two columns (imagine the first number is a counter and the second one is a test score for example).

Find the average (more precisely; the arithmetic mean: sum of numbers divided by how many numbers are there) of the numbers in the second column (find the average score).

Use exactly two digits to the right of the decimal point. i. e., use exactly two "decimal digits" without any rounding. Eg: if average = 21.349 , the solution is 21.34. If average = 33.1 , the solution is 33.10.

Save the solution in the /home/admin/solution file, for example: echo "123.45" > ~/solution

Tip: There's bc, Python3, Golang and sqlite3 installed in this VM.

Notes and solution:

First, we print the file to see what we are working with.

We see that the second column contains the data to compute, so we cut that column.

cat /home/admin/scores.txt | cut --delimiter " " --fields 2

where we use a space " " as a delimiter to indicate when a column ends, then, we select the second one with --fields 2.

After that, to sum all those rows, we first create a single string with + as a separator (using paste) so we can pass that output to the command bc to interpret and sum all the numbers.

cat /home/admin/scores.txt | cut --delimiter " " --fields 2 | paste -sd+ -

where the -s (serial) option makes paste display the lines on one file and the option -d+ makes the command join them all with a + sign.

cat /home/admin/scores.txt | cut --delimiter " " --fields 2 | paste -sd+ - | bc

we then pass that input to be interpreted by bc so it can be summed together.

Now that we have the sum of all numbers, we also need the total numbers so we can preform the arithmetic mean.

We can get the total number with the command wc -l to count lines.

cat /home/admin/scores.txt | wc -l

or, since we are given a numbered list, we can also use the last line of the first column.

cat /home/admin/scores.txt | cut --delimiter " " --fields 1 | tail -n 1

To get the average, well use the command bc with a precision of 2 decimals (scale=2) and configured so it uses a float format (-l).

cat /home/admin/scores.txt | cut --delimiter " " --fields 2 | paste -sd+ - | bc | xargs -I % sh -c "echo 'scale=2; %/100'" | bc -l

With this, we conclude that the answer is 5.20.