Append a vector as a row in a CSV file

Question

What I already have:

Consider the following data — just dummy data, the real data is created automatically:

features <- numeric(0)
features <- c(features, 1, 2, 3, 4, 5, 6)
features2 <- numeric(0)
features2 <- c(features2, 1, 2, 3, 4, 5, 6)
featureVectors <- list()
featureVectors[["file1"]] <- features
featureVectors[["file2"]] <- features2
resultMatrix <- do.call(rbind, featureVectors)
colnames(resultMatrix) <- c("SPEC_MEAN", "SPEC_SD", "SPEC_MODE", "AUTOC_MEAN", "AUTOC_SD", "ZC_MEAN")

This produces an output like the following:

      SPEC_MEAN SPEC_SD SPEC_MODE AUTOC_MEAN AUTOC_SD ZC_MEAN
file1         1       2         3          4        5       6
file2         1       2         3          4        5       6

I can write this to a CSV file by calling write.csv(resultMatrix, file="out.csv").

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What I need:

As the result file is (currently) just created on the fly, I'd like to write these features (i.e. the vectors) to the CSV file as soon they are evaluated.

So I thought I'd use write.csv and append, but the option isn't available for the method. I then thought I could use write.table, but there are two problems:

1. write.table does not indent the first empty column name, thus leaving my first row shifted one to the left.

2. The data is somehow incorrectly transposed. See example below.

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What I've tried:

Also, calling these commands …

write.table(resultMatrix, file="data-appended.csv", sep=",")
write.table(features, file="data-appended.csv", sep=",", append=TRUE, col.names=FALSE)

… produces this result:

"SPEC_MEAN","SPEC_SD","SPEC_MODE","AUTOC_MEAN","AUTOC_SD","ZC_MEAN"
"file1",1,2,3,4,5,6
"file2",1,2,3,4,5,6
"1",1
"2",2
"3",3
"4",4
"5",5
"6",6

… which is not what I want. So, how do I append the content of the features vector, including the file name, to an already existing CSV file?

Answer 1

Two adjustments will solve your two problems.

• To keep indentation of the column headers, use the unintuitive (but documented!) argument col.names=NA:

  write.table(resultMatrix, file = "data-appended.csv", sep = ",", 
              col.names = NA)
  

• To write features (a vector) as a row rather than a column, transpose it and convert it to a matrix before passing it to write.table():

  FF <- as.matrix(t(features))
  write.table(FF, file = "data-appended.csv", sep = ",", 
              col.names = FALSE, append=TRUE)