Count distinct values of a field in a file

OK, Assuming that your file is a text file, having the fields separated by comma separator ','. You would also know which field 'transactionid' is in terms of its position. Assuming that your 'transactionid' field is 7th field.

awk -F ',' '{print $7}' text_file | sort | uniq -c

This would count the distinct/unique occurrences in the 7th field and prints the result.

Maybe not the sleekest method, but this should work:

awk '{print $1}' your_file | sort | uniq | wc -l

where $1 is the number corresponding to the field to be parsed.

There is no need to sort the file .. (uniq requires the file to be sorted)
This awk script assumes the field is the first whitespace delimiited field.

awk 'a[$1] == "" { a[$1]="X" } END { print length(a) }' file