identifying a common observation across the groups

[kamalesh pahurkar]

How can I identify the common observations across the groups. I have a group codes under which there are different codes. I want to identify the codes that are common across the groups.

[Carlo Lazzaro]

Kamalesh:
If I got you right, you may want to consider something along the following lines:

. use "https://www.stata-press.com/data/r17/nlswork.dta"
(National Longitudinal Survey of Young Women, 14-24 years old in 1968)

. egen wanted=count( year) if year==70

[Eric Makela]

Hi Kamalesh,

This is effective for creating categorical variables for what you describe, even if not terribly elegant. The variable 'group3' identifies variables that are common across the first two groups. Note there are none. I don't wish to speak for Carlo, but he would suggest a more detailed description of your problem is necessary to properly contribute to Statalist and solve your actual problem.

sysuse auto
gen wtclass=(weight<2700)+2*(weight>=2700 & weight<3500)+3*(weight>=3500)
gen mpgclass=(mpg<20)+2*(mpg>=20 & mpg<28)+3*(mpg>=28)
egen group1=group(wtclass foreign)
egen group2=group(make mpgclass)
egen group3=group(group1 group2)

[kamalesh pahurkar]

Hi look, I have the following kind of data structure. I just want to keep or identify the product codes that are common across all the company code.

company code	product code
11	115
11	117
11	119
11	112
12	117
12	115
12	119
16	108
16	117
16	119
16	111
16	115
16	120
14	222
14	117
14	115
14	119

[Hemanshu Kumar]

Perhaps this?

clear
input int(company_code product_code)
11    115
11    117
11    119
11    112
12    117
12    115
12    119
16    108
16    117
16    119
16    111
16    115
16    120
14    222
14    117
14    115
14    119
end

egen int num_companies = count(company_code), by(product_code)
levelsof company_code, local(companies)
local tot_companies: word count `companies'

gen byte common_to_all = (num_companies == `tot_companies')

Then you can do things like

. tab product_code if common_to_all

product_cod |
          e |      Freq.     Percent        Cum.
------------+-----------------------------------
        115 |          4       33.33       33.33
        117 |          4       33.33       66.67
        119 |          4       33.33      100.00
------------+-----------------------------------
      Total |         12      100.00

This code assumes that each product_code appears only once for a given company_code. This is the case in your example, but if it is not true in the dataset, let me know and we'll find an alternative solution.

[kamalesh pahurkar]

Hi Hemanshu,Thannks for your response. It works. Can you tell me, what will be the change in syntax if I also have a time variable in the above dataset.