invalid variable name

[Haiyan Zeng]

Hi! I am trying to reshape my data.

id Co base ID3
103 0 0 103_6_6
104 0 1 104_0_0
104 0 0 104_1_1
104 0 0 104_3_3
104 0 0 104_6_6
104 1 0 104_12_12
106 1 0 106_1_1
106 1 0 106_3_3
106 1 0 106_6_6
106 1 0 106_12_12
106 1 0 106_99_18
106 1 0 106_24_24
106 1 0 106_36_36
107 0 1 107_0_-1
107 0 0 107_99_4
108 0 1 108_0_0
108 0 0 108_1_1

Here is my code:
reshape wide Co base, i(id) j(ID3) string

But I got this error message:
Co101_0_-1 invalid variable name

Why is it invalid?
Anyway, I drop this observation and run the code again. But I got an error message again:
Co107_0_-1 invalid variable name

Why is it invalid?
How to detect all the possible invalid names?
How can I reshape my data?
Thank you very much!

[Nick Cox]

Minus signs aren't allowed in variable names. Here's a work-around:

clear 
input id Co base str9 ID3
103 0 0 103_6_6
104 0 1 104_0_0
104 0 0 104_1_1
104 0 0 104_3_3
104 0 0 104_6_6
104 1 0 104_12_12
106 1 0 106_1_1
106 1 0 106_3_3
106 1 0 106_6_6
106 1 0 106_12_12
106 1 0 106_99_18
106 1 0 106_24_24
106 1 0 106_36_36
107 0 1 107_0_-1
107 0 0 107_99_4
108 0 1 108_0_0
108 0 0 108_1_1
end 

replace ID3 = subinstr(ID3, "-", "M", .) 

reshape wide Co base, i(id) j(ID3) string

foreach v of var *_*_* { 
    local label : var label `v'
    local label = subinstr("`label'", "M", "-", .)
    label var `v' "`label'"
} 
    
describe

[Haiyan Zeng]

Thank you so much! Indeed! It works now!