你要学会看帮助啊。stata帮助很好的都有解释。
要学会自己能解决问题。下面是stata中merge的帮助
help merge dialogs: merge
merge multiple
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Title
[D] merge -- Merge datasets
Syntax
merge [varlist] using filename [filename ...] [, options]
options description
--------------------------------------------------------------------------------------------------------------
Options
keep(varlist) keep only the specified variables from data in filename
_merge(newvar) newvar marks source of resulting observation; default is _merge
nolabel do not copy value label definitions from filename
nonotes do not copy notes from filename
update replace missing data in memory with data from filename
replace replace nonmissing data in memory with data from filename
nokeep drop observations in using dataset that do not match
nosummary drop summary variables when multiple filenames are specified
* unique match variables uniquely identify observations in both data in memory and in filename
* uniqmaster match variables uniquely identify observations in memory
* uniqusing match variables uniquely identify observations in filename
* sort sort master and using datasets by match variables before merge; sort implies unique if
uniqmaster or uniqusing is not specified
--------------------------------------------------------------------------------------------------------------
* unique, uniqmaster, uniqusing, and sort require varlist (the match variables) be specified.
Description
merge joins corresponding observations from the dataset currently in memory (called the master dataset) with
those from Stata-format datasets stored as filename (called the using datasets) into single observations. If
filename is specified without an extension, .dta is assumed.
merge can perform both one-to-one and match merges.
Options
+---------+
----+ Options +-----------------------------------------------------------------------------------------------
keep(varlist) specifies the variables to be kept from the using data. If keep() is not specified, all
variables are kept.
The varlist in keep(varlist) differs from standard Stata varlists in two ways: variable names in varlist
may not be abbreviated, except by the use of wildcard characters; and you may not refer to a range of
variables, such as price-weight.
_merge(newvar) specifies the name of the variable to be created that will mark the source of the resulting
observation. The default is _merge(_merge); that is, if you do not specify this option, the new variable
will be named _merge.
nolabel prevents Stata from copying the value label definitions from the using dataset into the result. Even
if you do not specify this option, label definitions from the using dataset do not replace label
definitions in the master dataset.
nonotes prevents notes in the using data from being incorporated into the result. The default is to
incorporate notes from the using data that do not already appear in the master dataset.
update specifies that the values from the using dataset be retained in cases where the master dataset contains
missing. By default, the master dataset is held inviolate -- values from the master dataset are retained
when the variables are found in both datasets.
replace, allowed with update only, specifies that even when the master dataset contains nonmissing values,
they are to be replaced with corresponding values from the using dataset when the corresponding values are
not equal. A nonmissing value, however, will never be replaced with a missing value.
nokeep causes merge to ignore observations in the using dataset that have no corresponding observation in the
master. The default is to add these observations to the merged result and mark such observations with
_merge==2.
nosummary causes merge to drop the summary variables created when multiple using datasets are specified. The
default is to create _merge1 recording results from merging the first disk dataset, _merge2 recording
results from merging the second disk dataset, and so on. _merge1, _merge2, ..., contain 1 if an
observation was found in the respective disk dataset and 0 otherwise.
Whether or not nosummary is specified, overall status variable _merge is created.
unique, uniqmaster, and uniqusing specify that the match variables in a match-merge uniquely identify the
observations. Match variables are required with unique, uniqmaster, and uniqusing.
unique specifies that the match variables uniquely identify the observations in the master dataset and in
the using dataset. For most match-merges, you should specify unique. merge does nothing differently when
you specify the option, unless the assumption you are making is false, in which case an error message is
issued and the data are not merged.
uniqmaster specifies that the match variables uniquely identify the observations in memory, the master
data, but not necessarily the ones in the using dataset.
uniqusing specifies that the match variables uniquely identify the observations in the using dataset, but
not necessarily the ones in the master dataset.
unique is thus equivalent to specifying uniqmaster and uniqusing.
Things are more complicated when multiple using datasets are specified. unique still means unique in all
datasets, and uniqusing still means unique in each of the using datasets, just as you would expect, but
uniqmaster takes on a whole new meaning: uniqmaster means unique in the master and in all using datasets
except the last! It asserts that the match variables uniquely identify observations in the master at each
step, meaning that when the master is merged with the first using dataset, then when the (new) master
(equal to original plus first using) is merged with the second using dataset, and so on. In summary,
uniqmaster is simply not useful when multiple using datasets are specified.
If none of the three unique options are specified, observations in neither the master nor the using
dataset are required to be unique, although they could be. If they are not unique, records that have the
same values of the match variables are joined by observation until all the records on one side or the
other are matched; after that, the final record on the shorter side is duplicated over and over again to
match with the remaining records needing to be matched on the longer side.
sort specifies that the master and using datasets be sorted by the match variables, before the datasets are
merged, if they are not already sorted by them. Match variables are required with sort. sort implies
unique if uniqmaster or uniqusing is not specified.
Remarks
merge can perform both one-to-one and match merges. In either case, the variable _merge (or the variable
specified in _merge() if provided) is added to the data containing
_merge==1 obs. from master data
_merge==2 obs. from only one using dataset
_merge==3 obs. from at least two datasets, master or using
update can be used only when there is one using file. When update is specified, the codes for _merge are
_merge==1 obs. from master data
_merge==2 obs. from using data
_merge==3 obs. from both, master agrees with using
_merge==4 obs. from both, missing in master updated
_merge==5 obs. from both, master disagrees with using
When multiple using files are specified, a set of summary variables is created, as long as nosummary is not
used. These summary variables are named _merge1 (related to the first using dataset), _merge2 (related to the
second using dataset), etc. (or, once again, the variable specified in _merge() if provided, followed by the
number of the using file). These variables will contain
_mergek==0 obs. not present in corresponding using dataset
_mergek==1 obs. present in corresponding using dataset
Variable labels identifying the dataset associated with each summary variable are attached to these summary
variables.
Examples
----------------------------------------------------------------------------------------------------------------
Setup
. webuse odd
. list
. webuse even1
. list
Perform one-to-one merge
. merge using http://www.stata-press.com/data/r10/odd
. list
----------------------------------------------------------------------------------------------------------------
Setup
. webuse even1, clear
Perform match-merge
. merge number using http://www.stata-press.com/data/r10/odd, sort
. list
. sort number
. list
----------------------------------------------------------------------------------------------------------------
Setup
. webuse autotech, clear
. describe
. describe using http://www.stata-press.com/data/r10/autocost
Perform match-merge
. merge make using http://www.stata-press.com/data/r10/autocost
. tabulate _merge
----------------------------------------------------------------------------------------------------------------
Setup
. webuse dollars, clear
. list
. webuse sforce
. list
Perform match-merge with spreading
. merge region using http://www.stata-press.com/data/r10/dollars
----------------------------------------------------------------------------------------------------------------
Setup
. webuse odd3, clear
. list
. webuse letter
. list
. webuse even
. list
Perform match-merge with multiple datasets
. merge number using http://www.stata-press.com/data/r10/odd3 http://www.stata-press.com/data/r10/letter
----------------------------------------------------------------------------------------------------------------
Setup
. webuse original, clear
. list
. webuse updates
. list
. webuse original
Update data with match-merge
. merge make using http://www.stata-press.com/data/r10/updates, update
. list
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Also see
Manual: [D] merge
Online: [D] append, [D] cross, [D] joinby, [D] save, [D] sort
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