从一个 CSV 复制 n 行并将它们粘贴到另一个 CSV 中 n 次

Question

I'm having a bit of a problem trying to figure this one out.

I have two CSV files, one of them without headers and the other with headers.

file1.csv (no headers):
apples
bananas

file2.csv (with headers):
HEADER1,HEADER2
item1,item3
item1,item3
item1,item3
item2,item3
item2,item3
item2,item3

I would like to create a new file: "file3.csv" where "apples" and "bananas" are listed the same number of times as "item1" and "item2" respectively.

The resulting file3.csv should look like this:

file3.csv
HEADER1,HEADER2,HEADER3
item1,item3,apples
item1,item3,apples
item1,item3,apples
item2,item3,bananas
item2,item3,bananas
item2,item3,bananas

To add the new header I'm using echo "$(head -n 1 file2.csv),HEADER3 >file3.csv .

To copy and paste the lines I've tried to do it with: awk -F, -v OFS=, 'NR==FNR {a[$1]=$1; next} {print $0,a[$1]}' file1.csv file2.csv awk -F, -v OFS=, 'NR==FNR {a[$1]=$1; next} {print $0,a[$1]}' file1.csv file2.csv but it doesn't work as I intend.

If an awk expert could help me a little, I would be eternally thankful.

Thanks!

Answer 1

golfed version

$ awk -F, -v OFS=, 'NR==FNR{a[NR+1]=$1;a[1]="HEADER3";next} $3=a[b[$1]=c+=!b[$1]]' file{1,2}.csv

HEADER1,HEADER2,HEADER3
item1,item3,apples
item1,item3,apples
item1,item3,apples
item2,item3,bananas
item2,item3,bananas
item2,item3,bananas

Answer 2

$ cat tst.awk
BEGIN { FS=OFS="," }
NR == FNR {
    idx2fruit[FNR] = $0
    next
}
!seen[$1]++ {
    item2idx[$1] = cnt++
}
{
    idx = item2idx[$1]
    fruit = (FNR > 1 ? idx2fruit[idx] : "HEADER3")
    print $0, fruit
}

$ awk -f tst.awk file1.csv file2.csv
HEADER1,HEADER2,HEADER3
item1,item3,apples
item1,item3,apples
item1,item3,apples
item2,item3,bananas
item2,item3,bananas
item2,item3,bananas

Answer 3

This might work for you (GNU sed):

sed -E '1{x;s/^/cat file1/e;s/$/\n/;x;s/$/,HEADER3/;b}
        2H;:a;G;/^([^,]*,).*\n\1/{s/\n([^\n]*).*/,\1/;b}
        x;s/^[^\n]*\n(.*)\n.*/\1/;x;s/\n.*//;H;ba' file2

Overview:

Keep file1 lines in the hold space and append them to lines from file2 . When the key changes in file2 pop off a line from file1 in the hold space and repeat.

NB The hold space doubles as a repository for lines from file1 and also stores the previous lines key from file2 .

Prime the hold space with records from file1 and append the third header.

Compare the current line with the previous and if the keys are the same, append the first line in the hold space of file1

Otherwise, delete the first line in the hold space of file1 and replace the key by the current lines key, remove the appended lines from the hold space on the the current line, then jump back and execute the previous instructions as to when the keys matched.