Use of count command - stata

Question

I am using a dataset, which among other variables includes the following:
. describe year country co brand
storage display value
variable name type format label variable label
----------------------------------------------------------------------------------------------------------------
year int %9.0g year (=first dimension of panel)
country byte %9.0g market market (=second dimension of panel)
co int %9.0g model code (=third dimension of panel)
brand byte %21.0g brand brand code
After I load the dataset, I generate a new variable and declare my data to be panel:
egen yearcountry = group(year country), label
xtset co yearcountry
I would like to estimate the market share of each brand in each country.
For example:
count if brand=="AlfaRomeo" & country=="Italy"
However, i get the following error:
type mismatch
r(109);
The entire dataset consisting of 11,483 observations can be downloaded from here.

Answer 1

The following works for me:
. count if brand == 1 & country == 4
111
The variables brand and country are not string but numeric with value labels:
. tabulate country
market |
(=second |
dimension |
of panel) | Freq. Percent Cum.
------------+-----------------------------------
Belgium | 2,641 23.00 23.00
France | 2,252 19.61 42.61
Germany | 2,281 19.86 62.47
Italy | 2,020 17.59 80.07
UK | 2,289 19.93 100.00
------------+-----------------------------------
Total | 11,483 100.00
. taulate country, nolabel
market |
(=second |
dimension |
of panel) | Freq. Percent Cum.
------------+-----------------------------------
1 | 2,641 23.00 23.00
2 | 2,252 19.61 42.61
3 | 2,281 19.86 62.47
4 | 2,020 17.59 80.07
5 | 2,289 19.93 100.00
------------+-----------------------------------
Total | 11,483 100.00
However, note that what you are calculating here is not the market share, but the number of cars of a particular brand in a certain country. The percentage market share is usually defined as the ratio of unit sales and total market unit sales.
The following code snippet will thus produce what you want:
forvalues i = 1 / 47 {
bysort year (country): egen a_`i' = total(brand == `i')
bysort year (country): gen b_`i' = (a_`i' / _N) * 100
}
collapse b_*, by(country year)
You can also check that the results add up as follows:
egen all = rowtotal(b_*)
You could then see the market share for AlfaRomeo & Audi, for years 1970 & 1976 and for Belgium & France as follows:
format b_* all %4.2f
list year country b_1 b_2 all if inlist(year,1970, 1976) & inlist(country, 1, 2), noobs
+---------------------------------------+
| year country b_1 b_2 all |
|---------------------------------------|
| 1970 Belgium 3.31 7.35 100.00 |
| 1976 Belgium 5.01 4.13 100.00 |
| 1970 France 3.31 7.35 100.00 |
| 1976 France 5.01 4.13 100.00 |
+---------------------------------------+