Replace NA values in dataframe variable with values from other dataframe by “ID”

Question

I would like to know if there is a more concise way to replace NA values for a variable in a dataframe than what I did below. The code below seems to be longer

Answer 1

At the stage where there is only (breaks, fsites, bps and) df1 around:

df1$Value <- ifelse(is.na(df1$Value), 
                            breaks$Value[match(df1$Break, breaks$Break)], df1$Value)

#> df1
#   Site Plot Break       Value
#1     1    0     1  0.39330965
#2     1    1     5  0.12465733
#3     1    2     7  0.27380161
#4     1    3     8  0.02728899
#5     1    4    11 42.00000000
#6     2    0     1  2.00000000
#7     2    1     6  0.43971253
#8     2    2    11  0.28972408
#9     3    0     1  0.03642906
#10    3    1     4  0.57746001
#11    3    2     6  0.82037592
#12    3    3     8  0.32321736
#13    3    4     9  0.28637503
#14    3    5    11 42.00000000

#just to test with your `df4`
> sort(df1$Value) == sort(df4$Value)
[1] TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE TRUE