How to get predictions from multiple fitted models

I have a data frame with calibration curves for multiple samples (signal s as a function of concentration c):

cal <- data.frame(sample = c(rep("A", 8), rep("B", 8), rep("C", 8)),
                  c_std = rep(c(0, 1, 5, 10, 25, 50, 100, 200), 3),
                  s_std = c(40341, 24196, 13403,  6956,  3000,  1507, 312, 12,
                            40261, 24250, 13537,  6977,  2940,  1465, 304, 12,
                            40075, 24469, 13696,  7060,  2972,  1487, 307, 12))

Additionally, I have a dataframe with observations made on the same samples:

obs <- data.frame(sample = c("A", "B", "C"),
                  s_sample = c(1364, 4726, 521))

First, I fit models for each calibration curve using drm from the library drc.

model <- function(df) drc::drm(c_std ~ s_std, fct = LL2.3(), data = df)

library(dplyr)

cal_models <- cal %>%
  group_by(sample) %>%
  nest() %>%
  mutate(model = map(data, model)) %>%
  unnest(sample) %>%
  distinct(sample, model)

From the obtained models I want to get predictions for the observations I made on my samples. This is where I'm stuck. My idea was to merge the two objects containing the models and the observations by the sample ID and then apply predict from the stats package in a similar way as I used to fit the models with map. I don't know how to do this, though. This is how I merge the data frames:

dat <- merge(cal_models, obs)

And this is my approach to get predictions from the models, just that I would like to do this in one step for all samples:

cal_A <- subset(cal, sample == "A")
model_A <- drc::drm(c_std ~ s_std, data = cal_A, fct = LL2.3()
predicted <- stats::predict(model_A, data.frame(obs$s_sample[1]))
predicted

Solution

It's probably easiest to make a list of models using your calibration data like this:

models <- by( cal , INDICES = cal$sample , FUN = model )

Then mapplying predict over your obs data as follows:

mapply( FUN = function(x, y) { predict(models[[x]], data.frame(y)) }, 
   x=obs$sample ,  
   y=obs$s_sample)

A.Prediction B.Prediction C.Prediction 
    45.09688     18.07154     79.75994

If instead you want to add this to the existing data frame:

cbind(obs, prediction=mapply( FUN = function(x, y) { predict(models[[x]], data.frame(y)) }, 
        x=obs$sample ,  
        y=obs$s_sample))

             sample s_sample prediction
A.Prediction      A     1364   45.09688
B.Prediction      B     4726   18.07154
C.Prediction      C      521   79.75994