help duplicates dialogs: report examples
list tag drop
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Title
[D] duplicates -- Report, tag, or drop duplicate observations
Syntax
Report duplicates
duplicates report [varlist] [if] [in]
List one example for each group of duplicates
duplicates examples [varlist] [if] [in] [, options]
List all duplicates
duplicates list [varlist] [if] [in] [, options]
Tag duplicates
duplicates tag [varlist] [if] [in] , generate(newvar)
Drop duplicates
duplicates drop [if] [in]
duplicates drop varlist [if] [in] , force
options description
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Main
compress compress width of columns in both table and
display formats
nocompress use display format of each variable
fast synonym for nocompress; no delay in output of
large datasets
abbreviate(#) abbreviate variable names to # characters;
default is ab(8)
string(#) truncate string variables to # characters;
default is string(10)
Options
table force table format
display force display format
header display variable header once; default is table
mode
noheader suppress variable header
header(#) display variable header every # lines
clean force table format with no divider or separator
lines
divider draw divider lines between columns
separator(#) draw a separator line every # lines; default is
separator(5)
sepby(varlist) draw a separator line whenever varlist values
change
nolabel display numeric codes rather than label values
Summary
mean[(varlist)] add line reporting the mean for each of the
(specified) variables
sum[(varlist)] add line reporting the sum for each of the
(specified) variables
N[(varlist)] add line reporting the number of nonmissing
values for each of the (specified) variables
labvar(varname) substitute Mean, Sum, or N for varname in last
row of table
Advanced
constant[(varlist)] separate and list variables that are constant
only once
notrim suppress string trimming
absolute display overall observation numbers when using
by varlist:
nodotz display numerical values equal to .z as field of
blanks
subvarname substitute characteristic for variable name in
header
linesize(#) columns per line; default is linesize(79)
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Menu
Data > Data utilities > Manage duplicate observations
Description
duplicates reports, displays, lists, tags, or drops duplicate
observations, depending on the subcommand specified. Duplicates are
observations with identical values either on all variables if no varlist
is specified or on a specified varlist.
duplicates report produces a table showing observations that occur as one
or more copies and indicating how many observations are "surplus" in the
sense that they are the second (third, ...) copy of the first of each
group of duplicates.
duplicates examples lists one example for each group of duplicated
observations. Each example represents the first occurrence of each group
in the dataset.
duplicates list lists all duplicated observations.
duplicates tag generates a variable representing the number of duplicates
for each observation. This will be 0 for all unique observations.
duplicates drop drops all but the first occurrence of each group of
duplicated observations. The word drop may not be abbreviated.
Any observations that do not satisfy specified if and/or in conditions
are ignored when you use report, examples, list, or drop. The variable
created by tag will have missing values for such observations.
Options for duplicates examples and duplicates list
+------+
----+ Main +-------------------------------------------------------------
compress, nocompress, fast, abbreviate(#), string(#); see [D] list.
+---------+
----+ Options +----------------------------------------------------------
table, display, header, noheader, header(#), clean, divider,
separator(#), sepby(varlist), nolabel; see [D] list.
+---------+
----+ Summary +----------------------------------------------------------
mean[(varlist)], sum[(varlist)], N[(varlist)], labvar(varname); see [D]
list.
+----------+
----+ Advanced +---------------------------------------------------------
constant[(varlist)], notrim, absolute, nodotz, subvarname, linesize(#);
see [D] list.
Option for duplicates tag
generate(newvar) is required and specifies the name of a new variable
that will tag duplicates.
Option for duplicates drop
force specifies that observations duplicated with respect to a named
varlist be dropped. The force option is required when such a varlist
is given as a reminder that information may be lost by dropping
observations, given that those observations may differ on any
variable not included in varlist.
Remarks
As of Stata 11, the browse subcommand is no longer available. To open
duplicates in the Data Browser, use the following commands:
. duplicates tag, generate(newvar)
. browse if newvar > 1
See [D] edit for details on the browse command.
Examples
Setup
. sysuse auto
. keep make price mpg rep78 foreign
. expand 2 in 1/2
Report duplicates
. duplicates report
List one example for each group of duplicated observations
. duplicates examples
List all duplicated observations
. duplicates list
Create variable dup containing the number of duplicates (0 if observation
is unique)
. duplicates tag, generate(dup)
List the duplicated observations
. list if dup==1
Drop all but the first occurrence of each group of duplicated
observations
. duplicates drop
List all duplicated observations
. duplicates list
Also see
Manual: [D] duplicates
Help: [D] codebook, [D] contract, [D] edit, [D] isid, [D] list
