How can I calculate an emperical CDF in R?
http://stackoverflow.com/questio ... -emperical-cdf-in-r
I'm reading a sparse table from a file which looks like:
1 0 7 0 0 1 0 0 0 5 0 0 0 0 2 0 0 0 0 1 0 0 0 1
1 0 0 1 0 0 0 3 0 0 0 0 1 0 0 0 1
0 0 0 1 0 0 0 2 0 0 0 0 1 0 0 0 1 0 1 0 0 1
1 0 0 1 0 3 0 0 0 0 1 0 0 0 1
0 0 0 1 0 0 0 2 0 0 0 0 1 0 0 0 1 0 1 0 0 1 1 2 1 0 1 0 1
Note row lengths are different.
Each row represents a single simulation. The value in the i-th column in each row says how many times value i-1 was observed in this simulation. For example, in the first simulation (first row), we got a single result with value '0' (first column), 7 results with value '2' (third column) etc.
I wish to create an average cumulative distribution function (CDF) for all the simulation results, so I could later use it to calculate an empirical p-value for true results.
To do this I can first sum up each column, but I need to take zeros for the undef columns.
How do I read such a table with different row lengths? How do I sum up columns replacing 'undef' values with 0'? And finally, how do I create the CDF? (I can do this manually but I guess there is some package which can do that).
Answers:
This will read the data in:
dat <- textConnection("1 0 7 0 0 1 0 0 0 5 0 0 0 0 2 0 0 0 0 1 0 0 0 1
1 0 0 1 0 0 0 3 0 0 0 0 1 0 0 0 1
0 0 0 1 0 0 0 2 0 0 0 0 1 0 0 0 1 0 1 0 0 1
1 0 0 1 0 3 0 0 0 0 1 0 0 0 1
0 0 0 1 0 0 0 2 0 0 0 0 1 0 0 0 1 0 1 0 0 1 1 2 1 0 1 0 1")
df <- data.frame(scan(dat, fill = TRUE, what = as.list(rep(1, 29))))
names(df) <- paste("Val", 1:29)
close(dat)
Resulting in:
> head(df)
Val 1 Val 2 Val 3 Val 4 Val 5 Val 6 Val 7 Val 8 Val 9 Val 10 Val 11 Val 12
1 1 0 7 0 0 1 0 0 0 5 0 0
2 1 0 0 1 0 0 0 3 0 0 0 0
3 0 0 0 1 0 0 0 2 0 0 0 0
4 1 0 0 1 0 3 0 0 0 0 1 0
5 0 0 0 1 0 0 0 2 0 0 0 0
....
If the data are in a file, provide the file name instead of dat. This code presumes that there are a maximum of 29 columns, as per the data you supplied. Alter the 29 to suit the real data.
We get the column sums using
df.csum <- colSums(df, na.rm = TRUE)
the ecdf() function generates the ECDF you wanted,
df.ecdf <- ecdf(df.csum)
and we can plot it using the plot() method:
plot(df.ecdf, verticals = TRUE)
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