awk: appending columns from multiple csv files into a single csv file - csv

Question

I have several CSV files (all have the same number of rows and columns). Each file follows this format:
1 100.23 1 102.03 1 87.65
2 300.56 2 131.43 2 291.32
. . . . . .
. . . . . .
200 213.21 200 121.81 200 500.21
I need to extract columns 2, 4 and 6, and add them to a single CSV file.
I have a loop in my shell script which goes through all the CSV files, extracts the columns, and appends these columns to a single file:
#output header column
awk -F"," 'BEGIN {OFS=","}{ print $1; }' "$input" > $output
for f in "$1"*.csv;
do
if [[ -f "$f" ]] #removes symlinks (only executes on files with .csv extension)
then
fname=$(basename $f)
arr+=("$fname") #array to store filenames
paste -d',' $output <(awk -F',' '{ print $2","$4","$6; }' "$f") > temp.csv
mv temp.csv "$output"
fi
done
Running this produces this output:
1 100.23 102.03 87.65 219.42 451.45 903.1 ... 542.12 321.56 209.2
2 300.56 131.43 291.32 89.57 897.21 234.52 125.21 902.25 254.12
. . . . . . . . . .
. . . . . . . . . .
200 213.23 121.81 500.21 231.56 5023.1 451.09 ... 121.09 234.45 709.1
My desired output is a single CSV file that looks something like this:
1.csv 1.csv 1.csv 2.csv 2.csv 2.csv ... 700.csv 700.csv 700.csv
1 100.23 102.03 87.65 219.42 451.45 903.1 542.12 321.56 209.2
2 300.56 131.43 291.32 89.57 897.21 234.52 125.21 902.25 254.12
. . . . . . . . . .
. . . . . . . . . .
200 213.23 121.81 500.21 231.56 5023.1 451.09 ... 121.09 234.45 709.1
In other words, I need a header row containing the file names in order to identify which files the columns were extracted from. I can't seem to wrap my head around how to do this.
What is the easiest way to achieve this (preferably using awk)?
I was thinking of storing the file names into an array, inserting a header row and then print the array but I can't figure out the syntax.

Answer 1

So, based on a few assumptions:
the inputs are called "*.csv" but they're actually whitespace-separated, as they appear.
the odd-numbered input columns just repeat the row number 3 times, and can be ignored
the column headings are just the filenames, repeated 3 times each
they are input to some other program, and the numbers are left-justified anyway, so you aren't particular about the column formatting (columns lining up, decimals aligned, ...)
Humble apologies because code PRE formatting is not working for me here
f=$(set -- *.csv; echo $*)
(echo $f; paste $f) |
awk 'NR==1 { for (i=1; i<=NF; i++) {x=x" "$i" "$i" "$i} }
NR > 1 { x=$1; for (i=2; i<= NF; i+=2) {x=x" "$i} }
{print x}'
hth