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  1. PO
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    <p>please find below a suggestion on how to potentially improve things a bit. Note that I'm providing a slightly more general example here such that others can easily reproduce.</p> <pre><code>require(XLConnect) # *** Generate some dummy files *** for(i in 1:10) { data = as.data.frame(matrix(rnorm(10000), ncol = 10)) names(data) = LETTERS[1:10] writeWorksheetToFile(file = sprintf("test%s.xls", i), data = data, sheet = "data", header = TRUE) } # *** Process files *** # Get files to process files = list.files(pattern = "^test[0-9]+.xls$") # Read chunks of data from files and subset data.negative = lapply(files, function(fl) { # Read data from file data = readWorksheetFromFile(file = fl, sheet = "data", header = TRUE) # Which rows have all values &lt; 0 idx = apply(data, 1, function(x) all(x &lt; 0)) data[idx,] }) # How many rows of all zeros does each chunk have? nrows = sapply(data.negative, nrow) # Combine data.negative into one data.frame data.negative = do.call(rbind, data.negative) # For each row add from which file it is originating data.negative$File = rep(files, times = nrows) # Write output file write.table(data.negative, file = "neg_val.txt", sep = "\t", quote = FALSE) </code></pre> <p>The idea is to NOT subsequently rbind the data.frames which makes things slow (depending on the size of your data.frames). In your case I would suggest doing the read and subset via lapply and then combine the subsets together for writing to a file. Also note that you can easily switch the lapply to e.g. plyr's llply and hook a parallel backend to it for parallelizing that task (however your disk might be a bottleneck if you attempt many parallel reads).</p> <p>Hope that helps.</p> <p>Best regards, Martin</p>
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    1. POPassing a list of files to XLConnect
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    1. USMartin Studer
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    1. COThanks for your help, and sorry for my stupidity, but I didn't get it to work so far. If i try to read in my files I'm getting the error message: `data.negative = lapply(files, function(fl) { + data = readWorksheetFromFil .... [TRUNCATED] Error in apply(data, 1, function(x) all(x < 0)) : dim(X) must have a positive length`. If I try to make `data = as.data.frame(readWorkSheetFromFile ...`, I'm getting no error message, but an empty file. Hope you can help once more!
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      1. USMarkus
    2. COWhat version of XLConnect are you using? The latest (0.1-9)?
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      1. USMartin Studer
    3. COI'm working with the latest R and package versions. Your example is running perfectly, by the way.
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