Replace last field with previous one

Question

I have a file that look like this one:

10-04-2022 00:39:13,36707,1455008753,32
11-05-2022 00:39:13,36708,1555008753,26
21-05-2022 00:39:13,36708,1555408753,15
12-06-2022 00:39:13,36709,1655008753

Because values into last field are related to running time of next line, I would like to shift down them to this way for using with gnuplot.

10-04-2022 00:39:13,36707,1455008753,
11-05-2022 00:39:13,36708,1555008753,32
21-05-2022 00:39:13,36708,1555408753,26
12-06-2022 00:39:13,36709,1655008753,15

Answer 1

A simple awk script could do this:

awk 'BEGIN {FS=OFS=","} { tmp=$NF; $NF=save; print; save=tmp; }' < input > output

This saves the fourth field into a temporary variable, replaces the fourth field with the previously-saved value, then prints the new line. Once printed, it saves the previous value of that fourth field for the next iteration. On the first line, the "save"d value is empty (the default awk behavior), which achieves the desired result.

The "BEGIN" section sets the Field Separator (used for splitting the input) and the Output Field Separator (used when printing the line/fields back out) to a comma. See your local awk man page, various online references, or the Open Group Base Specifications for awk to learn more.

Answer 2

Another awk solution, tested on GNU awk 5.1.0.

$ awk -F, -v OFS=, '{print $1,$2,$3,x;x=$NF}' myfile
10-04-2022 00:39:13,36707,1455008753,
11-05-2022 00:39:13,36708,1555008753,32
21-05-2022 00:39:13,36708,1555408753,26
12-06-2022 00:39:13,36709,1655008753,15
$

Answer 3

Using Raku (formerly known as Perl_6)

raku -e 'my @a = lines>>.split(","); my $m = @a>>.elems.max;  \
         .flat.join(",").put for [Z] @a>>.[0..$m-2], ("", @a>>.[$m-1]).flat;'

OR

raku -e 'my @a = lines.map: *.split(","); my $m = @a.map(*.elems).max;  \
         .flat.join(",").put for [Z] @a.map(*.[0..$m-2]), ("", @a.map: *.[$m-1]).flat;' 

This Raku answer is a little longer but is also more of a general solution, since the number of columns per row isn't hard-coded: a file-wide max is computed.

Briefly (both examples), lines are read-in, each split on , commas, and stored in @a array. A max number of elems (columns) is computed and stored as $m. Then Raku's [Z] "Zip Reduction" operator is used to pull off elements from the two lists that follow it one-by-one: these elements are flattened and joined back together in the output, such that now a "" empty string occupies the end of the first row, and subsequent @a[$m-1] indexed-values are moved down a row. Nota bene: Raku doesn't auto-flatten array elements, so you have to flatten them manually (if desired).

In the two examples I've tried to show how Raku's >> "hyper"-operator is similar to mapping a function/index over individual elements, either .map(*.fn) or (at the end of a method chain) using the colon form .map: *.fn;, which can reduce the number of parens required.

Sample Input:

10-04-2022 00:39:13,36707,1455008753,32
11-05-2022 00:39:13,36708,1555008753,26
21-05-2022 00:39:13,36708,1555408753,15
12-06-2022 00:39:13,36709,1655008753

Sample Output:

10-04-2022 00:39:13,36707,1455008753,
11-05-2022 00:39:13,36708,1555008753,32
21-05-2022 00:39:13,36708,1555408753,26
12-06-2022 00:39:13,36709,1655008753,15

---

Addendum: Here's another Raku approach, this time unwrapping the row/columns into individual elements, and reconstructing with rotor. It gives the exact same result as above:

raku -e 'my @a = lines>>.split(",").flat; my @b = @a[3,7,11...*];  \
         @a.=rotor(3 => 1); @a.=map(*.join(",")); @b.=unshift(""); \
        .join(",").put for [Z] @a, @b;' 

https://docs.raku.org/language/operators#index-entry-[]_(reduction_metaoperators)
https://docs.raku.org/language/operators#index-entry-hyper_method_call_operator
https://docs.raku.org/routine/flat

Answer 4

Using GNU sed 's extended regex mode to simplify regex composing, our approach is to maintain two lines at any time in the pattern space. Then move previous line's second last field to the current line end.

sed -E '
  1s/$/,/
  $!N
  s/(,[^,]+)(,[^,]*\n.*)/\2\1/
  P;D
' file

---

Input:-

10-04-2022 00:39:13,36707,1455008753,32
11-05-2022 00:39:13,36708,1555008753,26
21-05-2022 00:39:13,36708,1555408753,15
12-06-2022 00:39:13,36709,1655008753#

---

Output:-

10-04-2022 00:39:13,36707,1455008753,
11-05-2022 00:39:13,36708,1555008753,32
21-05-2022 00:39:13,36708,1555408753,26
12-06-2022 00:39:13,36709,1655008753#,15

---