= Mata =

Stata supports an interpreted language with a matrix-based data model called  '''Mata'''.

<<TableOfContents>>

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== Data Types ==

To instantiate a '''scalar''', the Mata concept for constants, try:

{{{
a=1
a="A"
}}}

To instantiate a '''row vector''', try:

{{{
f=(1,2,3)
f=(1::100)
f=("A","B","C")
}}}

Or for a '''column vector''', try:

{{{
g=(3\ 4 \5)
g=(1:100)
g=("A"\ "B"\ "C")
}}}

'''Matrices''' use the logical combination of this syntax.

{{{
h=(1,2,3\ 4,5,6\ 7,8,9)
h=("A","B"\ "C","D")
}}}

To combine vectors or matrices, try:

{{{
x=(1,2\ 6,7)
y=(3,4,5\ 8,9,10)
z=(x,y)
}}}



=== Matrix generation functions ===

''`J(r, c, a)`'' returns an ''`r x c`'' matrix with every element being ''`a`''.

''`I(r)`'' returns an ''`r x r`'' identity matrix.

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== Stata Interoperability ==



=== Reading data ===

To read data from Stata's active session into a matrix, try:

{{{
q=st_data(., "numeric_var_name")
r=st_data(., ("numeric_var_name"))
s=st_data(,. ("numeric_var_1", "numeric_var_2", "numeric_var_3"))
t=st_sdata(., ("string_var_name"))
}}}

Note that string data needs to be read using ''st_sdata'', not ''st_data''.

The omission of the first parameter ''(or rather, supplying the missing value as the first parameter)'' indicates that we want ''all'' rows.

The second parameter can similarly be omitted, though this isn't as useful. Column selectors can either me numeric indices or variable names. Note that selection by numeric indices is faster computationally.



=== Writing data ===

To write a matrix into a variable in Stata's active session, try:

{{{
st_store(., "numeric_var_name", numeric_matrix_name)
st_store(., ("numeric_var_name"), numeric_matrix_name)
st_store(., ("numeric_var_1", "numeric_var_2", "numeric_var_3"), numeric_matrix_name)
st_sstore(., "string_var_name", string_matrix_name)
}}}

Note that string data needs to be written using ''st_sstore'', not ''st_store''.

Parameters are specified in the same way as ''st_data''. Note that the function will raise an error if the selected matrix is not '''p-conformable''' ''(i.e. same dimensions)'' with the active session's data, so this flexibility is rarely useful.



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CategoryRicottone