[R] back tick names with predict function

[Rui Barradas]

Às 17:57 de 30/11/2023, Rui Barradas escreveu:
> Às 17:38 de 30/11/2023, Robert Baer escreveu:
>> I am having trouble using back ticks with the R extractor function 
>> 'predict' and an lm() model.  I'm trying too construct some nice 
>> vectors that can be used for plotting the two types of regression 
>> intervals.  I think it works with normal column heading names but it 
>> fails when I have "special" back-tick names.  Can anyone help with how 
>> I would reference these?  Short of renaming my columns, is there a way 
>> to accomplish this?
>>
>> Repex
>>
>> *# dataframe with dashes in column headings
>> cob =
>>    structure(list(`cob-wt` = c(212, 241, 215, 225, 250, 241, 237,
>>                              282, 206, 246, 194, 241, 196, 193, 224, 
>> 257, 200, 190, 208, 224
>> ), `plant-density` = c(137, 107, 132, 135, 115, 103, 102, 65,
>>                         149, 85, 173, 124, 157, 184, 112, 80, 165, 
>> 160, 157, 119)),
>> class = c("tbl_df", "tbl", "data.frame"), row.names = c(NA, -20L))
>>
>> # regression model works
>> mod2 = lm(`cob-wt` ~ `plant-density`, data = cob)
>>
>> # x sequence for plotting CI's
>> # Set up x points
>> x = seq(min(cob$`plant-density`), max(cob$`plant-density`), length = 
>> 1000)
>>
>> # Use predict to get CIs for a plot
>> # Add CI for regression line (y-hat uses 'c')
>> # usual trick is to assign x to actual x-var name in middle dataframe 
>> arguement
>> CI.c = predict(mod2, data.frame( `plant-density` = x), interval = 'c') 
>> # fail
>>
>> # Add CI for prediction value (y-tilde uses 'p')
>> # usual trick is to assign x to actual x-var name in middle dataframe 
>> arguement
>> CI.p = predict(mod2, data.frame(`plant-density`  = x), interval = 
>> 'p')    # fail
>> *
>>
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> Hello,
> 
> When creating the new data df, the default check.names = TRUE changes 
> the column name, it is repaired and the hyphen is replaced by a legal dot.
> 
> 
> # check.names defaults to TRUE
> newd <- data.frame(`plant-density` = x)
> # `plant-density` is not a column name
> head(newd)
> 
> # check.names set to FALSE
> newd <- data.frame(`plant-density` = x, check.names = FALSE)
> # `plant-density` is becomes a column name
> head(newd)
> 
> 
> # Use predict to get CIs for a plot
> # Add CI for regression line (y-hat uses 'c')
> # usual trick is to assign x to actual x-var name in middle dataframe 
> arguement
> CI.c = predict(mod2, newdata = newd, interval = 'confidence')  # fail
> 
> # Add CI for prediction value (y-tilde uses 'p')
> # usual trick is to assign x to actual x-var name in middle dataframe 
> arguement
> CI.p = predict(mod2, newdata = newd, interval = 'prediction')    # fail
> 
> 
> 
> Hope this helps,
> 
> Rui Barradas
> 
> 
Hello,

Sorry for the comments '# fail' in the last two instructions, I should 
have changed them.


CI.c <- predict(mod2, newdata = newd, interval = 'confidence')  # works
CI.p <- predict(mod2, newdata = newd, interval = 'prediction')  # works


Hoep this helps,

Rui Barradas


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