Hello all,

I strongly believe, that my issue is quite easy to resolve. However, I have
no idea how to find/debug what is wrong and I would blame myself for
insufficient knowledge about data tables and some useful functions in R! as
apply, sapply, lapply.

My question is as follows:

I would like to display correlation coefficients in a table (ideally - with
p-value, but below there's only Pearson correlation coefficients). However,
my code produces exactly the same values for each period (so something is
obviously wrong). Could you give me any advice:
    #first of all, I read my data table from CSV file:
    imported <- read.table (file="/home/someone/data_for_R.csv",
header=TRUE, sep='\t', quote='"\'', dec=',', fill=FALSE, comment.char="#",
na.strings = "NA", nrows = -1, skip = 0, check.names = TRUE, strip.white =
FALSE, blank.lines.skip = TRUE)

    # Typing: class(imported[["Period"]]) produces:
    # [1] "factor"

    #Typing: levels(imported[["Period"]]) produces:
    # [1] "Summer 2010" "Summer 2011" "Winter 2010" "Winter 2011" "Winter
2012"

    xx <- imported[c("Period","Data1.MEAN","Data2.MEAN")]
    result <- by(xx, xx$Period, function(x) {cor(xx$Data1.MEAN,
xx$Data2.MEAN)})
    result.dataframe <- as.data.frame(as.matrix(result))
    result.dataframe$C <- rownames(result)


Best regards,
Mateusz

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