# Using GLM programmatically
**URL:** https://discourse.julialang.org/t/using-glm-programmatically/30828
**Category:** General Usage
**Tags:** question, metaprogramming, glm
**Created:** [November 7, 2019, 1:19pm UTC](https://discourse.julialang.org/t/using-glm-programmatically/30828 "2019-11-07T13:19:35Z")
**Posts on this page:** 9
**Page:** 1
### Author:  [@Christopher\_Fisher](https://discourse.julialang.org/u/Christopher_Fisher)
#### Post date: [November 7, 2019, 1:19pm UTC](https://discourse.julialang.org/t/using-glm-programmatically/30828/1 "2019-11-07T13:19:35Z")
I would like to perform linear regression in a loop with variables. For example,
```julia
using DataFrames, GLM
data = DataFrame(X=[1,2,3], Y=[2,4,7])
var1 = :Y
var2 = :X
ols = lm(@formula($var1 ~ $var2), data)
```
I tried various approaches including the one proposed [here](https://discourse.julialang.org/t/iterating-on-regressions-using-glm/6686/3), which no longer works.
---
### Author:  [@xiaodai](https://discourse.julialang.org/u/xiaodai)
#### Post date: [November 7, 2019, 1:26pm UTC](https://discourse.julialang.org/t/using-glm-programmatically/30828/2 "2019-11-07T13:26:18Z")
Just add `@eval` in front
```julia
ols = lm(@eval(@formula($var1 ~ $var2)), data)
```
---
### Author:  [@Christopher\_Fisher](https://discourse.julialang.org/u/Christopher_Fisher)
#### Post date: [November 7, 2019, 1:29pm UTC](https://discourse.julialang.org/t/using-glm-programmatically/30828/3 "2019-11-07T13:29:13Z")
> [@xiaodai](#):
>
> ols = lm(@eval(@formula($var1 ~ $var2)), data)
Thank you! I tried something similar:
`ols = lm(@eval @formula($var1 ~ $var2) , data)`
I didn’t realize the parentheses were necessary.
---
### Author:  [@xiaodai](https://discourse.julialang.org/u/xiaodai)
#### Post date: [November 7, 2019, 1:30pm UTC](https://discourse.julialang.org/t/using-glm-programmatically/30828/4 "2019-11-07T13:30:24Z")
Ah, if you don’t add parenthesis then `@eval @formula($var1 ~ $var2) , data` doesn’t make sense for `@eval`, cos of the `,` which is captured by `@eval`.
---
### Author:  [@Christopher\_Fisher](https://discourse.julialang.org/u/Christopher_Fisher)
#### Post date: [November 7, 2019, 1:31pm UTC](https://discourse.julialang.org/t/using-glm-programmatically/30828/5 "2019-11-07T13:31:55Z")
Thanks for the explanation. At some point I should really learn how macros work.
---
### Author:  [@nilshg](https://discourse.julialang.org/u/nilshg)
#### Post date: [November 7, 2019, 1:39pm UTC](https://discourse.julialang.org/t/using-glm-programmatically/30828/6 "2019-11-07T13:39:02Z")
Just to add that the recommended approach to programmatically generating formula terms is by constructing the Term objects directly, as referenced in the StatsModels API here: [Modeling tabular data · StatsModels.jl](https://juliastats.org/StatsModels.jl/stable/formula/#Constructing-a-formula-programmatically-1)
---
### Author:  [@floswald](https://discourse.julialang.org/u/floswald)
#### Post date: [October 8, 2024, 7:39am UTC](https://discourse.julialang.org/t/using-glm-programmatically/30828/7 "2024-10-08T07:39:42Z")
I have a question: I need to have a squared term in the formula. I got the thing with `log` in the example [here](https://juliastats.org/StatsModels.jl/stable/formula/#Constructing-a-FunctionTerm-programmatically):
```julia
julia> log_term(t::AbstractTerm) = FunctionTerm(log, [t], :(log($(t))))
julia> lt = log_term(term(:a))
(a)->log(a)
julia> lt.f(9)
2.1972245773362196
```
but how do I use this to make a squared term?
```julia
julia> square_term(t::AbstractTerm) = FunctionTerm(^, [t], :(^($t,2)))
square_term (generic function with 2 methods)
julia> st = square_term(term(:b))
(b)->b ^ 2
julia> st.f(2)
ERROR: MethodError: no method matching ^(::Int64)
Closest candidates are:
^(::Integer, ::BigInt)
@ Base gmp.jl:655
^(::Integer, ::Bool)
@ Base bool.jl:170
^(::T, ::T) where T<:Integer
@ Base intfuncs.jl:310
...
Stacktrace:
[1] top-level scope
@ REPL[135]:1
julia> st.f(2,3)
8
```
I don’t get it.
---
### Author:  [@nilshg](https://discourse.julialang.org/u/nilshg)
#### Post date: [October 8, 2024, 7:59am UTC](https://discourse.julialang.org/t/using-glm-programmatically/30828/8 "2024-10-08T07:59:16Z")
I can have a quick look later to see if I can figure it out, but isn’t that the example in the docs?
[https://juliastats.org/StatsModels.jl/stable/internals/#An-example-of-custom-syntax:-poly](https://juliastats.org/StatsModels.jl/stable/internals/#An-example-of-custom-syntax:-poly)
---
### Author:  [@floswald](https://discourse.julialang.org/u/floswald)
#### Post date: [October 8, 2024, 8:13am UTC](https://discourse.julialang.org/t/using-glm-programmatically/30828/9 "2024-10-08T08:13:07Z")
yes that looks exactly like what I need. I think we should add the sentence to this example with the log function - I had no incentive to look any further, given that example.
> this is going to work only in cases with non-ambigous dispatch, for example, the log example below. For functions with multiple arguments you will need to extent the formula syntax as explained [there](https://juliastats.org/StatsModels.jl/stable/internals/#extending)