Help for generate

Title

[D] generate —

Create or change contents of variable

Syntax

Create new variable

generate [type] [ newvar[:lblname] =exp [if] [in] [, before(varname) | after(varname)]

Replace contents of existing variable

replace oldvar =exp [if] [in] [, nopromote]

Specify default storage type assigned to new variables

set type {float|double} [, permanently]

where type is one of
byte|int|long|float|double|str|str1|str2|...|str{ccl maxstrvarlen}

See Description below for an explanation of str. For the other types, see [D] data types.

by is allowed with generate and replace; see [D] by.

Menu

generate

Data > Create or change data > Create new variable

replace

Data > Create or change data > Change contents of variable

Description

generate creates a new variable. The values of the variable are specified by =exp.

If no type is specified, the new variable type is determined by the type of result returned by =exp. A float variable (or a double, according to set type) is created if the result is numeric, and a string variable is created if the result is a string. In the latter case, if the string variable contains values greater than 2,045 characters or contains values with a binary 0 (\0), a strL variable is created. Otherwise, a str# variable is created, where # is the smallest string that will hold the result.

If a type is specified, the result returned by =exp must be string or numeric according to whether type is string or numeric. If str is specified, a strL or a str# variable is created using the same rules as above.

See [D] egen for extensions to generate.

replace changes the contents of an existing variable. Because replace alters data, the command cannot be abbreviated.

set type specifies the default storage type assigned to new variables (such as those created by generate) when the storage type is not explicitly specified.

Options

before(varname) or after(varname) may be used with generate to place the newly generated variable in a specific position within the dataset. These options are primarily used by the Data Editor and are of limited use in other contexts. A more popular alternative for most users is order.

nopromote prevents replace from promoting the variable type to accommodate the change. For instance, consider a variable stored as an integer type (byte, int, or long), and assume that you replace some values with nonintegers. By default, replace changes the variable type to a floating point (float or double) and thus correctly stores the changed values. Similarly, replace promotes byte and int variables to longer integers (int and long) if the replacement value is an integer but is too large in absolute value for the current storage type. replace promotes strings to longer strings. nopromote prevents replace from doing this; instead, the replacement values are truncated to fit the current storage type.

permanently specifies that, in addition to making the change right now, the new limit be remembered and become the default setting when you invoke Stata.

Examples

---

Setup

webuse genxmpl3 

Create new variable age2 containing the values of age squared

generate age2 = age^2

---

Setup

webuse genxmpl3, clear 

Create variable age2 with a storage type of int and containing the values of age squared

generate int age2 = age^2

---

Setup

webuse genxmpl1, clear 

Replace the values in age2 with those of age^2

replace age2 = age^2

---

Setup

webuse genxmpl2, clear 

List the name variable

list name 

Create variable lastname containing the second word of name

generate lastname = word(name,2)

---

Setup

webuse genxmpl3, clear 

Create variable age2 with a storage type of int and containing the values of age squared for all observations for which age is more than 30

generate int age2 = age^2 if age > 30

---

Setup

webuse genxmpl4, clear 

Replace the value of odd in the third observation

replace odd = 5 in 3

---

Setup

webuse stan2, clear 

Create duplicate of every observation for which transplant is true (!=0)

expand 2 if transplant

Sort observations into ascending order of id

sort id 

Create variable posttran, with storage type of byte, equal to 1 for the second observation of each id and equal to 0 otherwise

by id: generate byte posttran = (_n==2) 

Create variable t1 equal to stime for the last observation of id

by id: generate t1 = stime if _n==_N

---