Dear R forum

I have a dataframe (of prices) as given below -

dat
 = data.frame(company = rep(c("A", "B", "C", "D", "index"), each = 5), 
prices = c(runif(5, 10, 12), runif(5, 108, 112), runif(5, 500, 510), 
runif(5, 40, 50), runif(5, 1000, 1020)))

   company     prices
1        A   10.61727
2        A   10.51892
3        A   11.80495
4        A   11.15243
5        A   10.77543
6        B  111.23817
7        B  109.19825
8        B 
 108.80053
9        B  110.79876
10       B  108.84385
11       C  504.71801
12       C  504.11778
13       C  502.89416
14       C  500.65996
15       C  502.26748
16       D   42.35901
17       D   43.71947
18       D   46.46092
19       D   43.62220
20       D   48.47480
21   index 1017.24476
22   index 1002.88139
23   index 1005.16148
24   index 1014.54480
25   index 1014.12103

I need to find the beta
 of A, B, C and D w.r.t index. 

Beta between two variables X and Y (where Y is dependent) is given by,

beta = coef(lm(Y ~ X))[2] 

Any guidance is appreciated.

With regards

Katherine
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