Calculating deltas

[Maroun Mezher]

Hello,

I have a list of manufacturers by period and I am trying to calculate a delta like so:

time_period	chocolate_type	manufacturer_count	delta
2011_Q1	White	3	--
2011_Q2	White	4	1
2011_Q3	White	4	0
2011_Q4	White	3	-1
2011_Q1	Dark	6	--
2011_Q2	Dark	8	2
2011_Q3	Dark	7	-1
2011_Q4	Dark	10	3

I have been trying to do

bysort chocolate_type time_period: gen delta = manufacturer_count[_N] - manufacturer_count[_N -1]

but keep getting syntax errors. Is there a way to do this in stata?

Thanks!

[Carlo Lazzaro]

Maroun:
what about:

bysort chocolate_type ( time_period): g diff= manufacturer_count[_n+1]- manufacturer_count[n]

[Maroun Mezher]

Hi Carlo, thank you. This works great!