Question

I need to read a .dat file using a .dct file. Has anyone done that using R?

The format is:

dictionary {
  # how many lines per record
  _lines(1)
  # start defining the first line
  _line(1)

  # starting column / storage type / variable name / read format / variable label
  _column(1)    str8    aid    %8s    "respondent identifier"
  ...
}

‘read formats’ are like:

%2f        2 column integer variable
%12s      12 column string variable
%8.2f      8 column number with 2 implied decimal places. 

Storage types are described here: http://www.stata.com/help.cgi?datatypes

Other sites used for info:

http://library.columbia.edu/indiv/dssc/technology/stata_write.html

http://www.stata.com/support/faqs/data-management/reading-fixed-format-data/

The .dat file is a bunch of numbers corresponding to the variables specified in the .dct file. (Presumably this is data in fixed width columns).

Here a real example:

.dtc file
http://goo.gl/qHZOk

data
http://goo.gl/FRGRF

A specific example from the stata site is:

The .dat file (“test.raw” in this instance)

C1245A101George Costanza
B1223B011Cosmo Kramer

The .dct file

dictionary using test2.raw {
 _column(1)     str5     code   %5s
 _column(2)     int      call   %4f
 _column(6)     str1     city   %1s
 _column(7)     int      neigh  %3f
 _column(10)    str16    name   %16s
}

The resulting data file:

      +-----------------------------------------------+
      |  code   call   city   neigh              name |
      |-----------------------------------------------|
   1. | C1245   1245      A     101   George Costanza |
   2. | B1223   1223      B      11      Cosmo Kramer |
      +-----------------------------------------------+

Answer 1

@thelatemail is spot-on about how to proceed. Here’s a small function I threw together to get you started on a more robust solution:

read.dat.dct <- function(dat, dct) {
    temp <- readLines(dct)
    pattern <- "_column\\(([0-9]+)\\)\\s+([a-z0-9]+)\\s+([a-z0-9_]+)\\s+%([0-9]+).*"
    classes <- c("numeric", "character", "character", "numeric")
    metadata <- setNames(lapply(1:4, function(x) {
        out <- gsub(pattern, paste("\\", x, sep = ""), temp)
        out <- gsub("^\\s+|\\s+$|.*\\{|\\}", "", out)
        out <- out[out != ""]
        class(out) <- classes[x] ; out }), 
                         c("StartPos", "Str", "ColName", "ColWidth"))
    read.fwf(dat, widths = metadata[["ColWidth"]], 
             col.names = metadata[["ColName"]])
}

There is still a lot you would have to do with respect to error checking, generalizing the function, and so on. For example, this function does not work with overlapping columns, as are present in the example that @thelatemail added to your question. Some error checking in the form of “StartPos[n] + ColWidth[n]” should equal “StartPos[n+1]” could be used to stop reading the file if this is not true with an error message. Additionally, the classes of the resulting data can also be extracted from the “metadata” list generated by the function and assigned in read.fwf using the colClasses argument.

Here is a dat file and a dct file to demonstrate:

Copy and paste the following two lines into a text editor and save it in your working directory as “test.dat”.

C1245A101George Costanza
B1223B011Cosmo Kramer

Copy and paste the following lines into a text editor and save it in your working directory as “test.dct”

dictionary using test.dat {
    _column(1)     str1     code   %1s
    _column(2)     int      call   %4f
    _column(6)     str1     city   %1s
    _column(7)     int      neigh  %3f
    _column(10)    str16    name   %16s
}

Now, run the function:

read.dat.dct(dat = "test.dat", dct = "test.dct")
#   code call city neigh            name
# 1    C 1245    A   101 George Costanza
# 2    B 1223    B    11    Cosmo Kramer

Update: An improved function (with still a lot of room for improvement)

read.dat.dct <- function(dat, dct, labels.included = "no") {
    temp <- readLines(dct)
    temp <- temp[grepl("_column", temp)]
    switch(labels.included,
           yes = {
               pattern <- "_column\\(([0-9]+)\\)\\s+([a-z0-9]+)\\s+(.*)\\s+%([0-9]+)[a-z]\\s+(.*)"
               classes <- c("numeric", "character", "character", "numeric", "character")
               N <- 5
               NAMES <- c("StartPos", "Str", "ColName", "ColWidth", "ColLabel")
           },
           no = {
               pattern <- "_column\\(([0-9]+)\\)\\s+([a-z0-9]+)\\s+(.*)\\s+%([0-9]+).*"
               classes <- c("numeric", "character", "character", "numeric")
               N <- 4
               NAMES <- c("StartPos", "Str", "ColName", "ColWidth")
           })
    metadata <- setNames(lapply(1:N, function(x) {
        out <- gsub(pattern, paste("\\", x, sep = ""), temp)
        out <- gsub("^\\s+|\\s+$", "", out)
        out <- gsub('\"', "", out, fixed = TRUE)
        class(out) <- classes[x] ; out }), NAMES)

    metadata[["ColName"]] <- make.names(gsub("\\s", "", metadata[["ColName"]]))

    myDF <- read.fwf(dat, widths = metadata[["ColWidth"]], 
             col.names = metadata[["ColName"]])
    if (labels.included == "yes") {
        attr(myDF, "col.label") <- metadata[["ColLabel"]]
    }
    myDF
}

How does it work with your data?

temp <- read.dat.dct(dat = "http://dl.getdropbox.com/u/18116710/21600-0009-Data.txt", 
                     dct = "http://dl.getdropbox.com/u/18116710/21600-0009-Setup.dct",
                     labels.included = "yes")
dim(temp)                     # How big is the dataset?
# [1] 180  40
head(temp[, 1:6])             # What do the first few columns & rows look like?
#   CASEID      AID RRELNO RPREGNO H3PC1.H3PC1 H3PC2.H3PC2
# 1      1 57118381      5       1           1           1
# 2      2 57134970      1       2           1           1
# 3      3 57135078      1       1           1           1
# 4      4 57135078      5       1           1           1
# 5      5 57164981      1       1           7           3
# 6      6 57191909      1       3           1           1
head(attr(temp, "col.label")) # What are the variable labels?
# [1] "CASE IDENTIFICATION NUMBER"             "RESPONDENT IDENTIFIER"                 
# [3] "ROMANTIC RELATIONSHIP NUMBER"           "RELATIONSHIP PREGNANCY NUMBER"         
# [5] "S23Q1 1 TOLD PARTNER PREGNANT-W3"       "S23Q2 MONTHS PREG WHEN TOLD PARTNER-W3"

What about with the original example?

read.dat.dct("test.dat", "test.dct", labels.included = "no")
#   code call city neigh            name
# 1    C 1245    A   101 George Costanza
# 2    B 1223    B    11    Cosmo Kramer