Awk script displaying incorrect output - awk

Question

I'm facing an issue in awk script - I need to generate a report containing the lowest, highest and average score for each assignment in the data file. The name of the assignment is located in column 3.
Input data is:
Student,Catehory,Assignment,Score,Possible
Chelsey,Homework,H01,90,100
Chelsey,Homework,H02,89,100
Chelsey,Homework,H03,77,100
Chelsey,Homework,H04,80,100
Chelsey,Homework,H05,82,100
Chelsey,Homework,H06,84,100
Chelsey,Homework,H07,86,100
Chelsey,Lab,L01,91,100
Chelsey,Lab,L02,100,100
Chelsey,Lab,L03,100,100
Chelsey,Lab,L04,100,100
Chelsey,Lab,L05,96,100
Chelsey,Lab,L06,80,100
Chelsey,Lab,L07,81,100
Chelsey,Quiz,Q01,100,100
Chelsey,Quiz,Q02,100,100
Chelsey,Quiz,Q03,98,100
Chelsey,Quiz,Q04,93,100
Chelsey,Quiz,Q05,99,100
Chelsey,Quiz,Q06,88,100
Chelsey,Quiz,Q07,100,100
Chelsey,Final,FINAL,82,100
Chelsey,Survey,WS,5,5
Sam,Homework,H01,19,100
Sam,Homework,H02,82,100
Sam,Homework,H03,95,100
Sam,Homework,H04,46,100
Sam,Homework,H05,82,100
Sam,Homework,H06,97,100
Sam,Homework,H07,52,100
Sam,Lab,L01,41,100
Sam,Lab,L02,85,100
Sam,Lab,L03,99,100
Sam,Lab,L04,99,100
Sam,Lab,L05,0,100
Sam,Lab,L06,0,100
Sam,Lab,L07,0,100
Sam,Quiz,Q01,91,100
Sam,Quiz,Q02,85,100
Sam,Quiz,Q03,33,100
Sam,Quiz,Q04,64,100
Sam,Quiz,Q05,54,100
Sam,Quiz,Q06,95,100
Sam,Quiz,Q07,68,100
Sam,Final,FINAL,58,100
Sam,Survey,WS,5,5
Andrew,Homework,H01,25,100
Andrew,Homework,H02,47,100
Andrew,Homework,H03,85,100
Andrew,Homework,H04,65,100
Andrew,Homework,H05,54,100
Andrew,Homework,H06,58,100
Andrew,Homework,H07,52,100
Andrew,Lab,L01,87,100
Andrew,Lab,L02,45,100
Andrew,Lab,L03,92,100
Andrew,Lab,L04,48,100
Andrew,Lab,L05,42,100
Andrew,Lab,L06,99,100
Andrew,Lab,L07,86,100
Andrew,Quiz,Q01,25,100
Andrew,Quiz,Q02,84,100
Andrew,Quiz,Q03,59,100
Andrew,Quiz,Q04,93,100
Andrew,Quiz,Q05,85,100
Andrew,Quiz,Q06,94,100
Andrew,Quiz,Q07,58,100
Andrew,Final,FINAL,99,100
Andrew,Survey,WS,5,5
Ava,Homework,H01,55,100
Ava,Homework,H02,95,100
Ava,Homework,H03,84,100
Ava,Homework,H04,74,100
Ava,Homework,H05,95,100
Ava,Homework,H06,84,100
Ava,Homework,H07,55,100
Ava,Lab,L01,66,100
Ava,Lab,L02,77,100
Ava,Lab,L03,88,100
Ava,Lab,L04,99,100
Ava,Lab,L05,55,100
Ava,Lab,L06,66,100
Ava,Lab,L07,77,100
Ava,Quiz,Q01,88,100
Ava,Quiz,Q02,99,100
Ava,Quiz,Q03,44,100
Ava,Quiz,Q04,55,100
Ava,Quiz,Q05,66,100
Ava,Quiz,Q06,77,100
Ava,Quiz,Q07,88,100
Ava,Final,FINAL,99,100
Ava,Survey,WS,5,5
Shane,Homework,H01,50,100
Shane,Homework,H02,60,100
Shane,Homework,H03,70,100
Shane,Homework,H04,60,100
Shane,Homework,H05,70,100
Shane,Homework,H06,80,100
Shane,Homework,H07,90,100
Shane,Lab,L01,90,100
Shane,Lab,L02,0,100
Shane,Lab,L03,100,100
Shane,Lab,L04,50,100
Shane,Lab,L05,40,100
Shane,Lab,L06,60,100
Shane,Lab,L07,80,100
Shane,Quiz,Q01,70,100
Shane,Quiz,Q02,90,100
Shane,Quiz,Q03,100,100
Shane,Quiz,Q04,100,100
Shane,Quiz,Q05,80,100
Shane,Quiz,Q06,80,100
Shane,Quiz,Q07,80,100
Shane,Final,FINAL,90,100
Shane,Survey,WS,5,5
awk script :
BEGIN {
FS=" *\\, *"
}
FNR>1 {
min[$3]=(!($3 in min) || min[$3]> $4 )? $4 : min[$3]
max[$3]=(max[$3]> $4)? max[$3] : $4
cnt[$3]++
sum[$3]+=$4
}
END {
print "Name\tLow\tHigh\tAverage"
for (i in cnt)
printf("%s\t%d\t%d\t%.1f\n", i, min[i], max[i], sum[i]/cnt[i])
}
Expected sample output:
Name Low High Average
Q06 77 95 86.80
L05 40 96 46.60
WS 5 5 5
Q07 58 100 78.80
L06 60 99 61
L07 77 86 64.80
When I run the script, I get a "Low" of 0 for all assignments which is not correct. Where am I going wrong? Please guide.

Answer 1

You can certainly do this with awk, but since you tagged this scripting as well, I'm assuming other tools are an option. For this sort of gathering of statistics on groups present in the data, GNU datamash often reduces the job to a simple one-liner. For example:
$ (echo Name,Low,High,Average; datamash --header-in -s -t, -g3 min 4 max 4 mean 4 < input.csv) | tr , '\t'
Name Low High Average
FINAL 58 99 85.6
H01 19 90 47.8
H02 47 95 74.6
H03 70 95 82.2
H04 46 80 65
H05 54 95 76.6
H06 58 97 80.6
H07 52 90 67
L01 41 91 75
L02 0 100 61.4
L03 88 100 95.8
L04 48 100 79.2
L05 0 96 46.6
L06 0 99 61
L07 0 86 64.8
Q01 25 100 74.8
Q02 84 100 91.6
Q03 33 100 66.8
Q04 55 100 81
Q05 54 99 76.8
Q06 77 95 86.8
Q07 58 100 78.8
WS 5 5 5
This says that for each group with the same value for the 3rd column (-g3, plus -s to sort the input (A requirement of the tool)) of simple CSV input (-t,) with a header (--header-in), display the minimum, maximum, and mean of the 4th column. It's all given a new header and piped to tr to turn the commas into tabs.

Answer 2

Your code works as-is with GNU awk. However, running it with the -t option to warn about non-portable constructs gives:
awk: foo.awk:6: warning: old awk does not support the keyword `in' except after `for'
awk: foo.awk:2: warning: old awk does not support regexps as value of `FS'
And running the script with a different implementation of awk (mawk in my case) does give 0's for the Low column. So, some tweaks to the script:
BEGIN {
FS=","
}
FNR>1 {
min[$3]=(cnt[$3] == 0 || min[$3]> $4 )? $4 : min[$3]
max[$3]=(max[$3]> $4)? max[$3] : $4
cnt[$3]++
sum[$3]+=$4
}
END {
print "Name\tLow\tHigh\tAverage"
PROCINFO["sorted_in"] = "#ind_str_asc" # gawk-ism for pretty output; ignored on other awks
for (i in cnt)
printf("%s\t%d\t%d\t%.1f\n", i, min[i], max[i], sum[i]/cnt[i])
}
and it works as expected on that other awk too.
The changes:
Using a simple comma as the field separator instead of a regex.
Changing the min conditional to setting to the current value on the first time this assignment has been seen by checking to see if cnt[$3] is equal to 0 (Which it will be the first time because that value is incremented in a later line), or if the current min is greater than this value.

Answer 3

another similar approach
$ awk -F, 'NR==1 {print "name","low","high","average"; next}
{k=$3; sum[k]+=$4; count[k]++}
!(k in min) {min[k]=max[k]=$4}
min[k]>$4 {min[k]=$4}
max[k]<$4 {max[k]=$4}
END {for(k in min) print k,min[k],max[k],sum[k]/count[k]}' file |
column -t
name low high average
Q06 77 95 86.8
L05 0 96 46.6
WS 5 5 5
Q07 58 100 78.8
L06 0 99 61
L07 0 86 64.8
H01 19 90 47.8
H02 47 95 74.6
H03 70 95 82.2