title: how can I resolve the "undefined columns selected" error for ggforest
body: <p>How can I resolve the error of undefined columns selected? I have loaded the survminer and the survival packages.</p>
  <pre><code>   cox4&lt;- coxph(formula= Surv(LOS,Mortality)~ BNPcat+HF_dx+Age+Sex+BMI+
             Admit_QTc+FI02_comb+Admit_Lactate,data=DF)
      ggforest(cox4)
  </code></pre>
  <pre><code>&gt; cox4
  Call:
  coxph(formula = Surv(LOS, Mortality) ~ BNPcat + HF_dx + Age + 
      Sex + BMI + Admit_QTc + FI02_comb + Admit_Lactate, data = DF)
  
                      coef  exp(coef)   se(coef)      z      p
  BNPcat1        0.9030311  2.4670696  0.9888592  0.913 0.3611
  HF_dx1         0.8819918  2.4157065  0.8519562  1.035 0.3005
  Age            0.0479344  1.0491018  0.0284893  1.683 0.0925
  Sex1           0.3792915  1.4612490  0.7020620  0.540 0.5890
  BMI            0.0250854  1.0254027  0.0319454  0.785 0.4323
  Admit_QTc     -0.0006391  0.9993611  0.0060206 -0.106 0.9155
  FI02_comb      0.0204957  1.0207072  0.0101321  2.023 0.0431
  Admit_Lactate  0.2433651  1.2755342  0.1112036  2.188 0.0286
  
  Likelihood ratio test=21.33  on 8 df, p=0.006311
  n= 71, number of events= 13 
     (62 observations deleted due to missingness)
  &gt; ggforest(cox4)
  Error in `[.data.frame`(cbind(allTermsDF, coef[inds, ]), , c(&quot;var&quot;, &quot;level&quot;,  : 
    undefined columns selected
  In addition: Warning message:
  In .get_data(model, data = data) :
    The `data` argument is not provided. Data will be extracted from model fit.
  </code></pre>