Issues reshaping data.frame from wide to long format

Question

I'm trying to reshape the below data frame into a long format, but I'm not having much luck writing the code using reshape() or melt().

                 pH                         SO4     
Lake  Lat   Long  1976   1977   1978  1981  1976  1977
1     58    7.2   4.59   -9999  4.48  4.63  6.5-  -9999
2     58.1  6.3   4.97   -9999  4.6   4.96  5.5-  -9999
4     58.5  7.9   4.32   4.23   4.4   4.49  4.8   6.5
5     58.6  8.9   4.97   4.74   4.98  5.21  7.4   7.6

I need to create a data frame where each row defines a unique combination of lake and year, columns for each chemical variable, and an additional column with the year of the measurement.

Answer 1

the melt() and cast() are too old.

More recently, the functions pivot_long() and pivot_wide() were introduced. (This functions replace gather() and spread() which replaced melt() and cast() )

Take a look at this