Sorting Irregular Data From CSV File?

im looking for a way to sort some data exported from an old stock recording software. the system outputs the data as a .csv file but each item bought is grouped into a particular heading, a line is only generated if money is spent under that particular heading. i cannot make the software generate lines if no money is spent so the number of lines generated each period changes.

period 1
3202 fuel £3000
3203 PPE £250
3204 major units £5000
3205 planned maint £212
3207 unplanned maint £457
period 2
3202 fuel £2500
3203 PPE £120
3204 major units £1000
3208 storage £212
3210 windows £457

if the data was regular i could simply add the totals each month and divide to get the average.

what i am looking for is a way to auto sort the data onto lines by possibly injecting the missing headings with zero as the total spent.