How do I compute the mean from ASCII file data in bash?

In bash I can grep some time measurements from a log file like this

grep "time:" myLogfile.txt | cut -d' ' -f 3 >> timeMeasurements.txt

#timeMeasurements.txt
2.5
3.5
2.0
...

Now I would like to compute the mean value from the values in timeMeasurements.txt. What is the quickest way to do that in bash?
I know that there is gnuplot and R but it seems like one has to write some lengthy script for either one on them.

Solution 1:

Obligatory GNU datamash version

$ datamash mean 1 < file
2.6666666666667

ASIDE: it feels like this really should be possible natively in bc (i.e. without using the shell, or an external program, to loop over input values). The GNU bc implementation includes a read() function - however it appears to be frustratingly difficult to get it to detect end-of-input. The best I could come up with is:

#!/usr/bin/bc

scale = 6
while( (x = read()) ) {
  s += x
  c += 1
}
s/c
quit

which you can then pipe file input to provided you terminate input with any non-numeric character e.g.

$ { cat file; echo '@'; } | ./mean.bc
2.666666

Solution 2:

You could use awk. Bash itself is not very good at maths...

awk 'BEGIN { lines=0; total=0 } { lines++; total+=$1 } END { print total/lines }' timeMeasurements.txt

Notes

• lines=0; total=0 set variables to 0
• lines++ increase lines by one for each line
• total+=$1 add the value in each line to the running total
• print total/lines when done, divide the total by the number of values

Solution 3:

Another way, using sed and bc:

sed 's/^/n+=1;x+=/;$ascale=1;x/n' timemeasurements.txt | bc

The sed expression converts the input to something like this:

n+=1;x+=2.5
n+=1;x+=3.5
n+=1;x+=2.0
scale=1;x/n

This is piped to bc which evaluates it line-by-line.