whatsnew7to8.hlp

是一个经济学管理应用软件 很难找的 但是经济学学生又必须用到

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44.  Existing commands {cmd:ci} and {cmd:summarize} have new option
     {cmd:separator(}{it:#}{cmd:)} that specifies how frequently separation
     lines should be inserted into the output; see help {help ci} and
     {help summarize}.

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45.  Existing command {cmd:impute} has three new options, {cmd:regsample},
     {cmd:all}, and {cmd:copyrest} that control the sample used for forming
     the imputation and how out-of-sample values are treated; see help
     {help impute}.

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46.  Existing command {cmd:collapse} now takes time-series operators; see help
     {help collapse}.


{title:What's new in data management}

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1.  New command {cmd:odbc} allows Stata for Windows to act as an ODBC client,
    meaning you can fetch data directly from ODBC sources; see help
    {help odbc}.

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2.  Existing command {cmd:generate} has new, more convenient syntax.
    Now you can type

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	{cmd:. generate a = 2 + 3}

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    or

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	{cmd:. generate b = "this" + "that"}

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    without specifying whether new variable {cmd:b} is numeric or string of a
    particular length.  If you wish, you can also type

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	{cmd:. generate str b = "this" + "that"}

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    which asserts that {cmd:b} is a string but leaves it to {cmd:generate} to
    determine the length of the string.  This is useful in programming
    situations because it helps to prevent bugs.  Of course, you can continue
    to type

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	{cmd:. generate double a = _pi/2}

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    and

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	{cmd:. generate str8 b = "this" + "that"}

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    See help {help generate}.

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3.  Existing command {cmd:list} has been completely redone.  Not only is
    output far more readable -- and even pretty -- but programmers will want
    to use {cmd:list} to format tables.  See help {help list}.

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4.  Existing command {cmd:merge} has been improved:

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    a.  New options {cmd:unique}, {cmd:uniqmaster}, and {cmd:uniqusing} ensure
	that the merge goes as you intend.  These options amount to assertions
	that, if false, cause {cmd:merge} to stop.  {cmd:unique} specifies
	that there should not be repeated observations within match variables,
	and that if you say "{cmd:merge} {it:id} {cmd:using} {it:myfile}",
	there should be one observation per {it:id} value in the master data
	(the data in memory) and one observation per {it:id} in the using
	data.  If observations are not unique, {cmd:merge} will complain.

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	Options {cmd:uniqmaster} and {cmd:uniqusing} make the same claim for
	one or the other half of the merge; {cmd:uniq} is equivalent to
	specifying {cmd:uniqmaster} and {cmd:uniqusing}.

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    b.  {cmd:merge} no longer has a limit on the number of match (key)
	variables.

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    c.  {cmd:merge} has new option {cmd:keep(}{it:varlist}{cmd:)} that
	specifies the variables to be kept from the using data.

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    See help {help merge}.

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5.  Existing command {cmd:append} has new option {cmd:keep(}{it:varlist}{cmd:)}
    that specifies the variables to be kept from the using data; see help
    {help append}.

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6.  New command {cmd:tsappend} appends observations in a time-series context.
    {cmd:tsappend} uses the information set by {help tsset}, automatically
    fills in the time variable, and fills in the panel variable if the panel
    variable was set.  See help {help tsappend}.

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7.  Existing command {cmd:describe using} will now allow you to specify a
    {it:varlist}, so you can check whether a variable exists in a dataset
    before merging or appending.  Programmers will be interested in the new
    {cmd:varlist} option, which will leave in {cmd:r()} the names of the
    variables in the dataset.  See help {help describe}.

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8.  New command {cmd:isid} verifies that a variable or set of variables
    uniquely identify the observations and so are suitable for use with
    {cmd:merge}; see help {help isid}.

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9.  Existing command {cmd:codebook} has new option {cmd:problems} to report
    potential problems in the data; see help {help codebook}.

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10.  New command {cmd:labelbook} is like {cmd:codebook}, but for value labels.
     In addition to providing documentation, the output includes a list of
     potential problems.

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     New command {cmd:numlabel} prefixes numerical values onto value labels
     and removes them.  For example, the mapping 2 --> "Catholic"
     becomes "2. Catholic" and vice versa.

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     See help {help labelbook} and {help numlabel}.

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11.  New command {cmd:duplicates} reports on, gives examples of, lists,
     browses, tags, and/or drops duplicate observations; see help
     {help duplicates}.

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12.  Existing command {cmd:recode} has three new features:

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     a.  {cmd:recode} now allows a {it:varlist} rather than a {it:varname},
	 so several variables can be recoded at once.

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     b.  {cmd:recode} has new option {cmd:generate()} to specify that the
	 transformed variables be stored under different names than the
	 originals.

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     c.  {cmd:recode} has new option {cmd:prefix()}, an alternative to
	 {cmd:generate}, to specify that the transformed variables are to be
	 given their original names, but with a prefix.

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     See help {help recode}.

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13.  Existing command {cmd:sort} has new option {cmd:stable} that says, within
     equal values of the sort keys, the observations are to appear in the same
     order as they did originally.  See help {help sort}.

{p 5 10 2}
14.  New command {cmd:webuse} loads the specified dataset, obtaining it over
     the web.  By default, datasets are obtained from
     {browse "http://www.stata-press.com/data/r8/"}, but you can reset that.
     See help {help webuse}.

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     New command {cmd:sysuse} loads the specified dataset that was shipped
     with Stata, plus any other datasets stored along the ado-path; see help
     {help sysuse}.

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15.  Existing command {cmd:insheet} has a new {cmd:delimiter(}{it:char}{cmd:)}
     option that allows you to specify an arbitrary character as the value
     separator; see help {help insheet}.

{p 5 10 2}
16.  Existing commands {cmd:infile} and {cmd:infix} no longer treat {cmd:^Z}
     as the end of a file; see help {help infile1}, {help infile2} and
     {help infix}.

{p 5 10 2}
17.  Existing command {cmd:save} has features:

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     a.  New option {cmd:orphans} specifies that all value labels, including
	 those not attached to any variables, are to be saved in the file.

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     b.  New option {cmd:emptyok} specifies that the dataset is to be saved
	 even if it contains no variables and no observations.

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     c.  Existing option {cmd:old} is removed.  To save datasets in Stata 7
	 format, use the new {cmd:saveold} command; see help {help saveold}.

{p 10 10 2}
     See help {help save}.  By the way, Stata 8 now has a single {cmd:.dta}
     dataset format used by both {help SpecialEdition:Stata/SE} and
     Intercooled Stata, meaning that sharing data with colleagues is easy.

{p 5 10 2}
18.  Existing command {cmd:outfile} has new features:

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     a.  New options {cmd:rjs} and {cmd:fjs} specify how strings are to be
	 aligned in the output file.  The default is left alignment.  Option
	 {cmd:rjs} specifies right alignment.  Option {cmd:fjs} specifies
	 alignment as specified by the variables' formats.

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     b.  New option {cmd:runtogether} is for use by programmers; it specifies
	 that all string variables be run together without extra spaces in
	 between or quotes.

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    See help {help outfile}.

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19.  You may attach value labels to the new extended missing values ({cmd:.a},
     {cmd:.b}, ..., {cmd:.z}); see help {help label}.

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20.  As a consequence of the 26 new missing value codes, the maximum value
     that can be stored in a {cmd:byte}, {cmd:int}, and {cmd:long} is reduced
     to 100, 32,740, and 2,147,483,620; see help {help datatypes}.

{p 5 10 2}
21.  New command {cmd:split} splits the contents of a string variable into one
     or more parts and is useful for separating words into multiple variables;
     see help {help split}.

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22.  In the way of minor improvements are

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     a.  Existing command {cmd:egen} now allows longer {it:numlists} in the
	 {cmd:values()} option for the {cmd:eqany()} and {cmd:neqany()}
	 functions; see help {help egen}.

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     b.  Existing command {cmd:destring} now allows an abbreviated
	 {it:newvarlist} in the {cmd:generate()} option; see help
	 {help destring}.

{p 10 14 2}
     c.  Existing commands {cmd:icd9} and {cmd:icd9p} have been updated to use
	 the V18 and V19 codes; V16, V18, and V19 codes have been merged so
	 that {cmd:icd9} and {cmd:icd9p} work equally well with old and new
	 datasets; see help {help icd9}.

{p 10 14 2}
     d.  Existing command {cmd:egen} {cmd:mtr()} has been updated to include
	 the marginal tax rates for the years 2000 and 2001; see help
	 {help egen}.

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     e.  Existing command {cmd:mvdecode}'s {cmd:mv()} option now allows a
	 {it:numlist}; see help {help mvencode}.

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     f.  Existing command {cmd:mvencode} has a new, more versatile syntax to
	 accommodate extended missing values; see help {help mvencode}.

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     g.  Existing command {cmd:xpose} has three new options: {cmd:format},
	 {cmd:format(%}{it:fmt}{cmd:)}, and {cmd:promote}.  The {cmd:format}
	 option finds the largest numeric display format in the pretransposed
	 data and applies it to the transposed data.  The
	 {cmd:format(%}{it:fmt}{cmd:)} option sets the transposed data to the
	 specified format.  The {cmd:promote} option causes the transposed
	 data to have the most compact numeric data type that preserves the
	 original data accuracy.  See help {help xpose}.

{p 10 14 2}
     h.  Existing command {cmd:notes} now allows the individual notes to
	 include SMCL directives; see help {help notes}.

{p 10 14 2}
     i.  Existing command {cmd:mkmat} has new {cmd:nomissing} option that
	 causes observations with missing values to be excluded (because
	 matrices can now contain missing values).  {cmd:mkmat} has also been
	 made faster.  See help {help mkmat}.

{p 10 14 2}
     j.  Existing command {cmd:ds} has three new options: {cmd:alpha},
	 {cmd:varwidth(}{it:#}{cmd:)}, and {cmd:skip(}{it:#}{cmd:)}.
	 {cmd:alpha} sorts the variables in alphabetic order.
	 {cmd:varwidth(}{it:#}{cmd:)} specifies the display width of the
	 variable names.  {cmd:skip(}{it:#}{cmd:)} specifies the number of
	 spaces between variables.  See help {help describe}.

{p 10 14 2}
     k. Existing commands {cmd:label dir} now returns the names of the defined
	value labels in {cmd:r(names)} and {cmd:label list} now returns the
	minimum and maximum of the mapped values in {cmd:r(min)} and
	{cmd:r(max)}; see help {help label}.


{title:What's new in expressions and functions}

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1.  First, a warning:  Do not type

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	{cmd:. generate} {it:newvar} {cmd:=} ... {cmd:if} {it:oldvar} {cmd:!= .}

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	{cmd:. replace} {it:oldvar} {cmd:=} ... {cmd:if} {it:oldvar} {cmd:!= .}

{p 14 18 2}
	{cmd:. list} ... {cmd:if} {it:var} {cmd:!= .}

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    Type

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	{cmd:. generate} {it:newvar} {cmd:=} ... {cmd:if} {it:oldvar} {cmd:< .}

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	{cmd:. replace} {it:oldvar} {cmd:=} ... {cmd:if} {it:oldvar} {cmd:< .}

{p 14 18 2}
	{cmd:. list} ... {cmd:if} {it:var} {cmd:< .}

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    or type

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	{cmd:. generate} {it:newvar} {cmd:=} ... {cmd:if !mi(}{it:oldvar}{cmd:)}

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	{cmd:. replace} {it:oldvar} {cmd:=} ... {cmd:if !mi(}{it:oldvar}{cmd:)}

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	{cmd:. list} ... {cmd:if !mi(}{it:var}{cmd:)}

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    Stata has new missing values and the ordering is {it:all numbers} <
    {cmd:.} < {cmd:.a} < {cmd:.b} < ... < {cmd:.z}.  If you do not use the new
    missing values, then your old habits will work, but better to be safe.

{p 10 10 2}
    It is a hot topic of debate at StataCorp whether {it:varname}{cmd:<.} or
    {cmd:!mi(}{it:varname}{cmd:)} is the preferred way of excluding missing
    values, and therefore both constructs are deemed to be equally stylish;