Counting Instance of a variable and returning average

[Emma Evans Student]

I am a student and new to Stata. Any help is appreciated.

I have a data set with age and weight. I would like to return a table that tells me the number of instances for each age and the average of the weight. Can someone point me in the right direction?

I have tried egen avgwt = mean(avgwt), by(age) and then summarizing the info but it just shows me number of observations and mean, std dev, etc for all observations. I need the average weight by each age and number of instances to use for some other calcs.

Thank you!

[William Lisowski]

Perhaps

collapse (count) N=weight (mean) weight, by(age)
list

will point you in a helpful direction.

[Nick Cox]

egen avgwt = mean(avgwt), by(age)
egen freq = count(avgwt), by(age) 
tabdisp age, c(avgwt freq)

will give a table with results either side. To use those results, you can collapse as William Lisowski

OR

egen tag = tag(age)

and carry out calculations

... if tag

[David Benson]

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(id age) int weight
 1  9  84
 2  9  98
 3  8  81
 4 11  75
 5 11 124
 6 11 119
 7 10 105
 8  9 101
 9  9  94
10  8 108
11 10 105
12 11 116
13  9  92
14 11 104
15  8 108
16 12  80
17  8 112
18 11 113
19  9  91
20 12  86
21  9 100
22  9 115
23 11 110
24  8 123
25 12 102
end

. tabulate age

        age |      Freq.     Percent        Cum.
------------+-----------------------------------
          8 |          5       20.00       20.00
          9 |          8       32.00       52.00
         10 |          2        8.00       60.00
         11 |          7       28.00       88.00
         12 |          3       12.00      100.00
------------+-----------------------------------
      Total |         25      100.00


. table age, c(n weight mean weight) row col

--------------------------------------
      age |    N(weight)  mean(weight)
----------+---------------------------
        8 |            5         106.4
        9 |            8        96.875
       10 |            2           105
       11 |            7       108.714
       12 |            3       89.3333
          |
    Total |           25        101.84
--------------------------------------


. table age, c(n weight mean weight median weight min weight max weight) row col format(%8.1fc)

--------------------------------------------------------------------------------
      age |    N(weight)  mean(weight)   med(weight)   min(weight)   max(weight)
----------+---------------------------------------------------------------------
        8 |            5         106.4         108.0          81.0         123.0
        9 |            8          96.9          96.0          84.0         115.0
       10 |            2         105.0         105.0         105.0         105.0
       11 |            7         108.7         113.0          75.0         124.0
       12 |            3          89.3          86.0          80.0         102.0
          | 
    Total |           25         101.8         104.0          75.0         124.0
--------------------------------------------------------------------------------