`model_parameters()` for `mgcv::gam()` returns an error when the model does not contain smooth terms

[RoelVerbelen]

Great set of packages!

I noticed an issue when trying to use it with mgcv: when specifying a gam() model without smooth terms, the model_parameters() function breaks down. Here's a reproducible example:

library(parameters)
library(mgcv)
#> Loading required package: nlme
#> This is mgcv 1.8-39. For overview type 'help("mgcv-package")'.

dat <- gamSim(1,n = 400, dist = "normal", scale = 2)
#> Gu & Wahba 4 term additive model
b <- gam(y~ x0 + x1 + x2 + x3, data = dat)

model_parameters(b, ci_method = "wald")
#> Error in rep("smooth_terms", nrow(cs.smooth)): invalid 'times' argument

^{Created on 2023-01-25 by the reprex package (v2.0.1)}

Would it be possible to take this use case into account?

[strengejacke]

library(parameters)
library(mgcv)
#> Loading required package: nlme
#> This is mgcv 1.8-41. For overview type 'help("mgcv-package")'.

set.seed(123)
dat <- gamSim(1,n = 400, dist = "normal", scale = 2)
#> Gu & Wahba 4 term additive model

b <- gam(y~ x0 + x1 + x2 + x3, data = dat)
model_parameters(b)
#> Parameter   | Coefficient |   SE |         95% CI | t(395) |      p
#> -------------------------------------------------------------------
#> (Intercept) |        6.51 | 0.54 | [ 5.44,  7.58] |  11.98 | < .001
#> x0          |        0.28 | 0.55 | [-0.80,  1.35] |   0.51 | 0.611 
#> x1          |        6.39 | 0.53 | [ 5.34,  7.44] |  11.97 | < .001
#> x2          |       -5.20 | 0.55 | [-6.29, -4.11] |  -9.39 | < .001
#> x3          |        1.40 | 0.54 | [ 0.34,  2.47] |   2.60 | 0.010

b <- gam(y~ s(x0) + s(x1), data = dat)
model_parameters(b)
#> # Fixed Effects
#> 
#> Parameter   | Coefficient |   SE |       95% CI | t(393.94) |      p
#> --------------------------------------------------------------------
#> (Intercept) |        7.97 | 0.17 | [7.64, 8.30] |     47.83 | < .001
#> 
#> # Smooth Terms
#> 
#> Parameter        |     F |   df |      p
#> ----------------------------------------
#> Smooth term (x0) |  4.48 | 2.53 | 0.004 
#> Smooth term (x1) | 43.35 | 2.53 | < .001

b <- gam(y ~ s(x0) + s(x1) - 1, data = dat)
model_parameters(b)
#> Parameter        | Coefficient | 95% CI | t(397.26) |      p
#> ------------------------------------------------------------
#> Smooth term (x0) |        1.50 |        |      0.53 | 0.628 
#> Smooth term (x1) |        1.24 |        |     14.24 | < .001

b <- gam(y ~ s(x0) + s(x1) + x2 + x3, data = dat)
model_parameters(b)
#> # Fixed Effects
#> 
#> Parameter   | Coefficient |   SE |         95% CI | t(391.73) |      p
#> ----------------------------------------------------------------------
#> (Intercept) |        9.88 | 0.39 | [ 9.11, 10.65] |     25.31 | < .001
#> x2          |       -5.30 | 0.53 | [-6.34, -4.25] |     -9.96 | < .001
#> x3          |        1.41 | 0.52 | [ 0.39,  2.43] |      2.71 | 0.007 
#> 
#> # Smooth Terms
#> 
#> Parameter        |     F |   df |      p
#> ----------------------------------------
#> Smooth term (x0) |  6.69 | 2.50 | < .001
#> Smooth term (x1) | 49.63 | 2.76 | < .001

^{Created on 2023-01-25 with reprex v2.0.2}

[strengejacke]

Requires latest insight

[RoelVerbelen]

Excellent, thanks a lot for the quick fix!