sum distance timecost if var28==1&membergender==1

if |

if &

if !

能不能查查帮助啊

或者把基础的书先看看。

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help for if                                                                manual:  [U] 14 Language syntax
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if qualifier

        command if exp

    exp in the syntax diagram means an expression, such as age>21.  See help exp for an explanation of
    expressions.

    There is another if used in Stata programming; see help ifcmd.

Description

    if at the end of a command means the command is to use only the data specified.  if is allowed with
    most Stata commands.

Examples

    . list make mpg if mpg>25

    . list make mpg if mpg>25 & mpg<30

    . list make mpg if mpg>25 | mpg<10

    . regress mpg weight displ if foreign==1

    Note that equality tests are performed by ==, not a single =; see help operators.

Also see

    Manual:  [U] 14 Language syntax

    Online:  help for language; by, in

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