[R] Evaluating a formula

[Chel Hee Lee]

You may use 'eval()' with 'parse()' if you wish to use 'formula()' as below:

 > a <- params[[1]]
 > b <- params[[2]]
 > eval(parse(text=func1))
   [1]   5.000000   5.652893   6.338843   7.057851   7.809917   8.595041
   [7]   9.413223  10.264463  11.148760  12.066116  13.016529  14.000000
  [13]  15.016529  16.066116  17.148760  18.264463  19.413223  20.595041
  [19]  21.809917  23.057851  24.338843  25.652893  27.000000  28.380165
  [25]  29.793388  31.239669  32.719008  34.231405  35.776860  37.355372
  [31]  38.966942  40.611570  42.289256  44.000000  45.743802  47.520661
  [37]  49.330579  51.173554  53.049587  54.958678  56.900826  58.876033
  [43]  60.884298  62.925620  65.000000  67.107438  69.247934  71.421488
  [49]  73.628099  75.867769  78.140496  80.446281  82.785124  85.157025
  [55]  87.561983  90.000000  92.471074  94.975207  97.512397 100.082645
  [61] 102.685950 105.322314 107.991736 110.694215 113.429752 116.198347
  [67] 119.000000 121.834711 124.702479 127.603306 130.537190 133.504132
  [73] 136.504132 139.537190 142.603306 145.702479 148.834711 152.000000
  [79] 155.198347 158.429752 161.694215 164.991736 168.322314 171.685950
  [85] 175.082645 178.512397 181.975207 185.471074 189.000000 192.561983
  [91] 196.157025 199.785124 203.446281 207.140496 210.867769 214.628099
  [97] 218.421488 222.247934 226.107438 230.000000
 >

Or, you can define your own function as below:

 > fn <- function(x, a, b)a*x^2 + b*x
 > fn(x=x, a=params[[1]], b=params[[2]])
   [1]   5.000000   5.652893   6.338843   7.057851   7.809917   8.595041
   [7]   9.413223  10.264463  11.148760  12.066116  13.016529  14.000000
  [13]  15.016529  16.066116  17.148760  18.264463  19.413223  20.595041
  [19]  21.809917  23.057851  24.338843  25.652893  27.000000  28.380165
  [25]  29.793388  31.239669  32.719008  34.231405  35.776860  37.355372
  [31]  38.966942  40.611570  42.289256  44.000000  45.743802  47.520661
  [37]  49.330579  51.173554  53.049587  54.958678  56.900826  58.876033
  [43]  60.884298  62.925620  65.000000  67.107438  69.247934  71.421488
  [49]  73.628099  75.867769  78.140496  80.446281  82.785124  85.157025
  [55]  87.561983  90.000000  92.471074  94.975207  97.512397 100.082645
  [61] 102.685950 105.322314 107.991736 110.694215 113.429752 116.198347
  [67] 119.000000 121.834711 124.702479 127.603306 130.537190 133.504132
  [73] 136.504132 139.537190 142.603306 145.702479 148.834711 152.000000
  [79] 155.198347 158.429752 161.694215 164.991736 168.322314 171.685950
  [85] 175.082645 178.512397 181.975207 185.471074 189.000000 192.561983
  [91] 196.157025 199.785124 203.446281 207.140496 210.867769 214.628099
  [97] 218.421488 222.247934 226.107438 230.000000
 >

Is this what you are looking for?  I hope this helps.

Chel Hee Lee

On 01/16/2015 02:16 AM, philippe massicotte wrote:
> Hi all.
>
> How we evaluate a formula in R?
>
> Ex.:
>
> params <- list(a = 2, b = 3)
> x <- seq(1,10, length.out = 100)
>
> func1 <- as.formula("y ~ a*x^2 + b*x")
>
> ##How to evaluate func1 using x and the params list
> ???
>
>
> Thank you in advance,
> Phil
>
>   		 	   		
> 	[[alternative HTML version deleted]]
>
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