New variable which combines the values of other variables together

[Jad Tamimi]

Hello, I have the following dataset,

* Example generated by -dataex-. For more info, type help dataex
clear
input byte tinh long macs byte capso
1   1 1
1   2 1
1   3 1
1   4 1
1   5 1
1   6 1
1   7 1
1   8 1
1   9 1
1  10 1
1  11 1
1  12 1
1  13 1
1  14 1
1  16 1
1  17 1
1  18 1
1  19 1
1  20 1
1  21 1
1  23 1
1  24 1
1  25 1
1  26 1
1  27 1
1  28 1
1  29 1
1  30 1
1  31 1
1  33 1
1  34 1
1  35 1
1  36 1
1  38 1
1  39 1
1  40 1
1  41 1
1  42 1
1  43 1
1  44 1
1  45 1
1  46 1
1  47 1
1  48 1
1  49 1
1  50 1
1  51 1
1  52 1
1  53 1
1  54 1
1  56 1
1  57 1
1  58 1
1  59 1
1  60 1
1  61 1
1  62 1
1  63 1
1  64 1
1  65 1
1  67 1
1  69 1
1  70 1
1  71 1
1  72 1
1  73 1
1  74 1
1  75 1
1  76 1
1  77 1
1  78 1
1  79 1
1  81 1
1  82 1
1  83 1
1  84 1
1  85 1
1  86 1
1  87 1
1  89 1
1  90 1
1  91 1
1  92 1
1  93 1
1  94 1
1  95 1
1  96 1
1  97 1
1  98 1
1  99 1
1 100 1
1 101 1
1 103 1
1 104 1
1 105 1
1 106 1
1 107 1
1 108 1
1 109 1
1 110 1
end

In this dataset the combination of the three variables above (tinh, macs, capso) uniquely identifies the observations, however to make later coding easier, I want to create a new variable called say 'id' which basically combines those variables in a consistent order, for example combining 'tinh' then 'macs' then 'capso'. So the new variable would take the value 111 for the first entry above , for the last entry it would take the value 11101. Hopefully thats enough to understand what I'm trying to do.

Any ideas how to implement this?

Thanks,
Jad

[Rich Goldstein]

try this:

gen str5 id=(strofreal(tinh)+strofreal(macs)+strofreal(capso))

[Nick Cox]

or

egen id = concat(tinh macs capso)

is an alternative. Adding spaces would ensure that e.g. 1 110 1 and 11 10 1 don't map to the same identifier.

See also https://journals.sagepub.com/doi/pdf...867X0800700407

[Hemanshu Kumar]

For some purposes, it is better to have numeric id variables. For instance, if you want id-level fixed effects and thus anticipate wanting to use Stata's automated factor variable capabilities -- something like regress y x i.id

If so, you might instead want

gen id = tinh * 10000 + macs * 10 + capso

which assumes that macs is no more than 3 digits and capso no more than 1 digit. You can change it appropriately if there are more digits in either of these.