Stata 15 help for duplicates

[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 ------------------------------------------------------------------------- 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 value of 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) -------------------------------------------------------------------------

Menu

duplicates report, duplicates examples, and duplicates list

Data > Data utilities > Report and list duplicated observations

duplicates tag

Data > Data utilities > Tag duplicated observations

duplicates drop

Data > Data utilities > Drop duplicated 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 > 0

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

Video example

How to identify and remove duplicate observations

Stored results

duplicates report, duplicates examples, duplicates list, duplicates tag, and duplicates drop store the following in r():

Scalars r(N) number of observations

duplicates report also stores the following in r():

Scalars r(unique_value) number of unique observations

duplicates drop also stores the following in r():

Scalars r(N_drop) number of observations dropped


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