Steve Fraser wrote:
>Assume the following variation on the auto data:
>
>Manuf Brand Model MPG Cost ....
>Ford Merc Mountaineer
>Ford Ford Explorer
>Ford Ford Escape
>GM GM Yukon
>GM Chev Tahoe
>Chry Dodge Durango
>Chry Dodge Durango
>Ford Ford Escape
>Ford Ford Escape
>GM Chev Blazer
>
>I am trying to capture the number of models offered by the 'brand' Ford as
>opposed to the 'manufacturer' Ford. If I sort by brand (assuming only one
>manufacturer for now..I will complicate with more manufacturers) and then
>tab brand and model, I get results depicting the frequency of each model
>(i.e. Explorer 1, Escape 3 for 'brand' Ford and Mountaineer 1 for 'brand'
>Merc). What I need is to capture the value '2' indicating 2 models for the
>'brand' Ford and '1' indicating 1 model for the 'brand' Merc. The only way
>I have been able to capture this is when I add the 'matcell' command (help
>from a FAQ) and then capturing the number of rows. However, even while I am
>currently only using one 'manufacturer', I have several 'brands' and need
>the number of models offered by each 'brand', but matrix will only return
>the matrix for the last 'brand' and matrix cannot be used with by. The
>>> Here is a brute force way that seems to work (if I understand your problem correctly):
. sort brand model
.
. by brand model: keep if _n == 1
(3 observations deleted)
.
. egen no_models = count(1), by(brand)
.
. l
manuf brand model no_models
1. GM Chev Blazer 2
2. GM Chev Tahoe 2
3. Chry Dodge Durango 1
4. Ford Ford Escape 2
5. Ford Ford Explorer 2
6. GM GM Yukon 1
7. Ford Merc Mountaineer 1
You may want to keep only the first record of each brand-model pair as each has the number of models for that brand. You may also want to drop both manuf & model as well since they are kind of artifacts from the exercise.
Eric
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Eric G. Wruck
Econalytics
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Columbus, OH 43209
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