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2009 Nov 16
3
Sum over indexed value
I am sure this is easy but I am not finding a function to do this.
I have two columns in a matrix. The first column contains multiple entries
of numbers from 1 to 100 (i.e. 10 ones, 8 twos etc.). The second column
contains unique numbers. I want to sum the numbers in column two based on
the indexed values in column one (e.g. sum of all values in column two
associated with the value 1 in column
2009 Nov 05
2
Using a by() function to process several regression (lm()) functions
Hello,
Thank you very much for looking at this. I have a "seasonal" user for R. I
teach my undergrads and graduates students statistics using R and often find
myself trying to solve problems to process student collected data in an
efficient way.
In this case, I have a data.frame with multiple observations. These are gas
concentrations in a chamber and are used to measure into rates,