### Re: Efficient way to sum columns in a file

by tlm (Prior)
 on Apr 13, 2005 at 11:55 UTC ( #447331=note: print w/replies, xml ) Need Help??

in reply to Efficient way to sum columns in a file

By testing eof() instead of eof in dave0's one-liner, you can extend its functionality to sum across multiple files. Like this:

```# First we make to test files
% perl -le 'print join(",", map int(rand(1000)), 1..10) for 1..50' > i
+n1.csv
% perl -le 'print join(",", map int(rand(1000)), 1..10) for 1..50' > i
+n2.csv
94,434,249,267,649,367,572,579,498,369
452,735,420,543,832,198,28,86,67,382
801,339,978,859,85,719,758,89,191,377

# Now we run dave0's original script on them
perl -lanF, -e '\$sum += \$F[6]; print "Sum is \$sum" if eof' in1.csv in2
+.csv
Sum is 23789
Sum is 48874

# Now let's try a small change --------------------------.
#                                                        |
#                                                        V
perl -lanF, -e '\$sum += \$F[6]; print "Sum is \$sum" if eof()' in1.csv i
+n2.csv
Sum is 48874
What happens is that eof (no parens!) returns true at the end of each file in @ARGV, while eof() is true only at the end of the last one (see eof). In the case of a single input file, the behavior is the same as before.

To get subtotals, you'd do

```perl -lanF, -e '\$total += \$F[6]; \$sub += \$F[6]; print "Subtotal: \$sub"
+ and \$sub = 0 if eof; print "Total: \$total" if eof()' in1.csv in2.csv
Subtotal: 23789
Subtotal: 25085
Total: 48874

An alternative to testing for eof(), is to put everything in an END. e.g.

```perl -lanF, -e '\$sum += \$F[6]; END{ print "Sum is \$sum" }' in1.csv in2
+.csv

Update: Bug in last one-liner corrected.

the lowliest monk

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Re^2: Efficient way to sum columns in a file
by Anonymous Monk on Apr 13, 2005 at 13:48 UTC
I don't think the '\$total += \$sub += \$F6;' part is doing what you expect it to... Actually, it doesn't add \$F6 to both \$total and \$sub, but rather add it to \$sub and then add \$sub to \$total, which generates a wrong total.

The totals was obviously wrong; that should have alerted me to the error. Thank you very much!

the lowliest monk

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