Stata 15 help for datatypes
[D] data types  Quick reference for data types
Description
This entry provides a quick reference for data types allowed by Stata.
See [U] 12 Data for details.
Remarks
Closest to
Storage 0 without
type Minimum Maximum being 0 bytes

byte 127 100 +/1 1
int 32,767 32,740 +/1 2
long 2,147,483,647 2,147,483,620 +/1 4
float 1.70141173319*10^38 1.70141173319*10^38 +/10^38 4
double 8.9884656743*10^307 8.9884656743*10^307 +/10^323 8

Precision for float is 3.795x10^8.
Precision for double is 1.414x10^16.
String
storage Maximum
type length Bytes

str1 1 1
str2 2 2
... . .
... . .
... . .
str2045 2045 2045
strL 2000000000 2000000000

Each element of data is said to be either type numeric or type string.
The word "real" is sometimes used in place of numeric. Associated with
each data type is a storage type.
Numbers are stored as byte, int, long, float, or double, with the default
being float. byte, int, and long are said to be of integer type in that
they can hold only integers.
Strings are stored as str#, for instance, str1, str2, str3, ..., str2045,
or as strL. The number after the str indicates the maximum length of the
string. A str5 could hold the word "male", but not the word "female"
because "female" has six characters. A strL can hold strings of
arbitrary lengths, up to 2000000000 characters, and can even hold binary
data containing embedded \0 characters.
Stata keeps data in memory, and you should record your data as
parsimoniously as possible. If you have a string variable that has
maximum length 6, it would waste memory to store it as a str20.
Similarly, if you have an integer variable, it would be a waste to store
it as a double.
Precision of numeric storage types
floats have about 7 digits of accuracy; the magnitude of the number does
not matter. Thus, 1234567 can be stored perfectly as a float, as can
1234567e+20. The number 123456789, however, would be rounded to
123456792. In general, this rounding does not matter.
If you are storing identification numbers, the rounding could matter. If
the identification numbers are integers and take 9 digits or less, store
them as longs; otherwise, store them as doubles. doubles have 16 digits
of accuracy.
Stata stores numbers in binary, and this has a second effect on numbers
less than 1. 1/10 has no perfect binary representation just as 1/11 has
no perfect decimal representation. In float, .1 is stored as
.10000000149011612. Note that there are 7 digits of accuracy, just as
with numbers larger than 1. Stata, however, performs all calculations in
double precision. If you were to store 0.1 in a float called x and then
ask, say, list if x==.1, there would be nothing in the list. The .1 that
you just typed was converted to double, with 16 digits of accuracy
(.100000000000000014...), and that number is never equal to 0.1 stored
with float accuracy.
One solution is to type list if x==float(.1). The float() function
rounds its argument to float accuracy. The other alternative would be
store your data as double, but this is probably a waste of memory. Few
people have data that is accurate to 1 part in 10 to the 7th. Among the
exceptions are banks, who keep records accurate to the penny on amounts
of billions of dollars. If you are dealing with such financial data,
store your dollar amounts as doubles.
