drop.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

{smcl}
{* 25mar2005}{...}
{cmd:help drop}, {cmd:help keep}, {cmd:help clear}{right:dialogs:  {dialog drop_vars:keep/drop variables}   }
{right: {dialog drop_obs:keep/drop observations}}
{hline}

{title:Title}

{p2colset 5 18 20 2}{...}
{p2col :{hi:[D] drop} {hline 2}}Eliminate variables or observations{p_end}
{p2colreset}{...}


{title:Syntax}

{p 8 13 2}{cmd:drop} {varlist}

{p 8 13 2}{cmd:drop} {help if:{bf:if} {it:exp}}

{p 8 13 2}{cmd:drop} {help in:{bf:in} {it:range}} [{help if:{bf:if} {it:exp}}]

{p  8 13 2}{cmd:keep} {varlist}

{p 8 13 2}{cmd:keep} {help if:{bf:if} {it:exp}}

{p 8 13 2}{cmd:keep} {help in:{bf:in} {it:range}} [{help if:{bf:if} {it:exp}}]

{p 8 13 2}{cmd:clear}

{phang}
{cmd:by} may be used with the second syntax of {cmd:drop} and the second
syntax of {cmd:keep}; see {helpb by}.


{title:Description}

{pstd}
{cmd:drop} eliminates variables or observations from the data in memory.

{pstd}
{cmd:keep} works the same as {cmd:drop}, except that you specify the
variables or observations to be kept rather than the variables or observations
to be deleted.

{pstd}
{cmd:clear} is equivalent to typing

{p2colset 9 34 36 2}{...}
{p2col :{cmd:. version {ccl stata_version}}}{p_end}
{p2col :{cmd:. drop _all}}{p_end}
{p2col :{cmd:. label drop _all}}(see {helpb label}){p_end}
{p2col :{cmd:. scalar drop _all}}(see {helpb scalar}){p_end}
{p2col :{cmd:. matrix drop _all}}(see {helpb matrix drop:matrix}){p_end}
{p2col :{cmd:. cluster drop _all}}(see {helpb cluster drop:cluster}){p_end}
{p2col :{cmd:. eq drop _all}}{p_end}
{p2col :{cmd:. constraint drop _all}}(see {helpb constraint}){p_end}
{p2col :{cmd:. postutil clear}}(see {helpb postutil}){p_end}
{p2col :{cmd:. _return drop _all}}(see {helpb _return}){p_end}
{p2col :{cmd:. discard}}(see {helpb discard}){p_end}
{p2col :{cmd:. mata: mata clear}}(see {helpb mata clear}){p_end}
{p2colreset}{...}


{title:Examples}

    {cmd:. drop if age<21}
    {cmd:. drop in 1/33}

    {cmd:. keep if age>=21}
    {cmd:. keep in 34/l}

    {cmd:. sort site}
    {cmd:. by site:  keep if _n==1}

    {cmd:. clear}


{title:Also see}

{psee}
Manual:  {bf:[D] drop}
{p_end}