Subtract with previous index where index is not a number using awk

i would like to subtract values from previous values but a condition must be satisfied. File: 2022-02-01 01:00:00|abc|2001|5 2022-02-01 01:00:00|abc|2002|10 2022-02-01 01:01:00|abc|2001|6 2022-02-01 01:01:00|abc|2002|11 2022-02-01 01:02:00|abc|2001|10 2022-02-01 01:02:00|abc|2002|11 2022-02-01 01:02:00|abc|2003|2 Desired output: 2022-02-01 01:00:00|abc|2001|5 2022-02-01 01:00:00|abc|2002|10 2022-02-01 01:01:00|abc|2001|1 2022-02-01 01:01:00|abc|2002|1 2022-02-01 01:02:00|abc|2001|4 2022-02-01 01:02:00|abc|2002|0 2022-02-01 01:02:00|abc|2003|2 I tried with awk but couldnt reach the previous index to subtract the value awk -F"|" 'BEGIN{OFS="|"}{a[$1,$2,$3]=$4}END{for (i in a) print i, a[i]-a[i-1] }' file