R: Create an iterator for splitting binary or character input...

imstrsplit {iotools} | R Documentation

## Create an iterator for splitting binary or character input into a matrix

### Description

`imstrsplit` takes a binary connection or character vector (which is interpreted as a file name) and splits it into a character matrix according to the separator.

### Usage

    imstrsplit(x, sep="|", nsep=NA, strict=TRUE, ncol = NA,
              type=c("character", "numeric", "logical", "integer",  "complex",
                     "raw"), max.line = 65536L, max.size = 33554432L)

### Arguments

`x` | character vector (each element is treated as a row) or a raw vector (LF characters `'\n'` separate rows) to split
`sep` | single character: field (column) separator. Set to `NA` for no seperator; in other words, a single column.
`nsep` | row name separator (single character) or `NA` if no row names are included
`strict` | logical, if `FALSE` then `mstrsplit` will not fail on parsing errors, otherwise input not matching the format (e.g. more columns than expected) will cause an error.
`ncol` | number of columns to expect. If `NA` then the number of columns is guessed from the first line.
`type` | a character string representing one of the 6 atomic types: `'character'`, `'numeric'`, `'logical'`, `'integer'`, `'complex'`, or `'raw'`. The output matrix will use this as its storage mode and the input will be parsed directly into this format without using intermediate strings.
`max.line` | maximum length of one line (in byets) - determines the size of the read buffer, default is 64kb
`max.size` | maximum size of the chunk (in bytes), default is 32Mb

### Details

If the input is a raw vector, then it is interpreted as ASCII/UTF-8 content with LF (`'\n'`) characters separating lines. If the input is a character vector then each element is treated as a line.

If `nsep` is specified then all characters up to (but excluding) the occurrence of `nsep` are treated as the row name. The remaining characters are split using the `sep` character into fields (columns). If `ncol` is `NA` then the first line of the input determines the number of columns. `mstrsplit` will fail with an error if any line contains more columns then expected unless `strict` is `FALSE`. Excessive columns are ignored in that case. Lines may contain fewer columns in which case they are set to `NA`.

The processing is geared towards efficiency - no string re-coding is performed and raw input vector is processed directly, avoiding the creation of intermediate string representations.

Note that it is legal to use the same separator for `sep` and `nsep` in which case the first field is treated as a row name and subsequent fields as data columns.

### Value

A matrix with as many rows as they are lines in the input and as many columns as there are fields in the first line. The storage mode of the matrix will be determined by the input to `type`.

### Author(s)

Michael Kane

### Examples

      mm <- model.matrix(~., iris)
      f <- file("iris_mm.io", "wb")
      writeBin(as.output(mm), f)
      close(f)
      it <- imstrsplit("iris_mm.io", type="numeric", nsep="\t")
      iris_mm <- it$nextElem()
      print(head(iris_mm))

      ## remove iterator, connections and files
      rm("it")
      gc(FALSE)
      unlink("iris_mm.io")

[Package iotools version 0.3-1 Index]