calculate the difference

[buunaanaa]

I am totally NEW.
I have a CSV file, I only have Sales, I need to calculate the amt change which is (day2 Sales) - (day1 Sales)
I need to add all the positive change and add only the negative together for the past 6 days data.

so, in the end, it would look like this:

------------------------------------------------

Output:
Sales	amt change	add only 	add only 
374.440002		positive	negitive
381.420013	6.980	past 6 changes	
391.540009	10.120		
390.75	0.790		
384.73999	6.010		
395.859985	11.120		
391.929993	3.930	4.703333667	1.788335167
374.519989	17.410	3.5399985	4.6900025
369.040009	5.480	1.8533325	5.6033325
364.940002	4.100	1.8533325	6.154998833
370.160004	5.220	2.723332833	5.1533305
379.640015	9.480	2.450002167	5.1533305
375.459991	4.180	2.450002167	5.1950025
381.720001	6.260	3.493337167	2.293335167

----------------------------------------------------

Here is my code

counter_1=1
data['amt change']=0

if (counter_1<=40) :
    data.ix[counter_1,'amt change'] =data.ix[counter_1,'Sales']-data.ix[counter_1-1,'Sales']
    counter_1 = counter_1+1
    print(x)
    
    print(counter_1)
    
    
    
data[['amt change']].head(20)
    
    print(counter_1)

i cannot pass this point.
Please help.


I dont have a website for a picture to this one. if anyone can tell me any img uploading resources, pelase let me know.
Many thanks.

[buunaanaa]

update the desired output

Output:
Sales	amt change	add only 	add only 
374.440002		positive	negitive
381.420013	6.980	past 6 changes	
391.540009	10.120		
390.75	    -0.790		
384.73999	-6.010		
395.859985	11.120		
391.929993	-3.930	4.703333667	1.788335167
374.519989	-17.410	3.5399985	4.6900025
369.040009	-5.480	1.8533325	5.6033325
364.940002	-4.100	1.8533325	6.154998833
370.160004	5.220	2.723332833	5.1533305
379.640015	9.480	2.450002167	5.1533305
375.459991	-4.180	2.450002167	5.1950025
381.720001	6.260	3.493337167	2.293335167