help mergeall
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Title

    mergeall -- A safe way to merge many files

Syntax

        mergeall varlist using folder [, options]

varlist is the match variables that uniquely identify observations. It is requi
> red.

    options               Description
    -------------------------------------------------------------------------
      csv                 files to be merged are .csv (default)
      txt                 files to be merged are .txt
      dta                 files to be merged are .dta
      tab                 insheet tab delimited data
      comma               insheet comma delimited data
      double              insheet all numeric variables as double. See format
      format              specify a format to be used in the event that a
                            numberic variable must be converted to string.
                            See tostring and format
      do(filename)        runs the specified do file on each individual file
                            before merging
      strings(varlist)    force the varlist to string format and all others
                            to numeric
      force               forces conversion to string or numeric. Required
                            with the string option.
      showsource          generates a new string variable containing the name
                            of the file each observation was drawn from.
    -------------------------------------------------------------------------


Description

    mergeall merges all of the files in a folder without loss of data due to
    variable storage types or duplicate unique identifiers.

Remarks

    mergeall loops through all of the files in the folder you specify,
    checking variable types before merging.  It sets all variables that are
    string in any file to be string in every file to prevent loss of data. By
    default, Stata forces the variable type of the master file on the using
    file, which can result in lost data.

    mergeall requires a unique identifier to be specified and exits with
    error if the identifier is not unique within files.  A unique identifier
    is required because Stata can sometimes merge in unexpected ways when
    there is no unique identifier, and the goal of mergeall is to make
    merging many files super-safe.

    mergeall Performs 1 to 1 merges using Stata10 style merging and creates a
    new variable, _disagreement, which equals 1 if an observation exists in
    two or more datasets, and the datasets disagree on its value.  If
    _disagreement equals 1, you have lost information.

    If you are so inclined, you can run a cleaning .do file on each dataset
    before merging using do(filename) (this is useful for fixing errors in
    unique identifiers, for example).

    strings is probably a bad idea because it can result in the loss of data,
    but if you are very sure you won't lose data, it runs a little faster.

    The showsource option is useful for troubleshooting when you want to
    return to the raw data to check values, but you don't know which raw file
    contains the observation you are looking for.

Also see

    Online:  [D] merge [D] append, [D] cross, [D] joinby, [D] save, [D] sort

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