Vector

Create

Action	Code	Details
From matrix	to_vector(m)	Type of vector depends on shape of the matrix?
From 1D array	real a[] = {1, 2}; to_vector(a)

Create column vector

Action	Code	Details
Declare column vector of size N	vector[N] v;
Declare column vector with values	vector[3] v = [3, 5, 7]'
Declare column vector filled with zeros	vector[N] v = rep_vector(0, N);
Declare column vector filled with value	vector[N] v = rep_vector(value, N);

Create row vector

Action	Code	Details
Declare row vector of size N	row_vector[N] v;
Declare row vector with values	row_vector[3] v = [3, 5, 7];

Create special vectors with constraints

Action	Code	Details
Declare ordered vector of size N	ordered[N] v;
Declare positive ordered vector of size N	positive_ordered[N] v;
Declare simplex of size N (proportions vector that sum up to 1)	simplex[N] theta;
Declare unit vector	unit_vector[N] theta;
Declare optional vector in parameter block, conditional on include	vector[include ? N : 0] v;	Useful for disabling model feature to save memory

Properties

Action	Code	Details
Length (number of elements)	num_elements(v)

Extract

Action	Code	Details
Get element at index i	v[i]
Get element at index i as vector	rep_vector(v[i], 1)
Get index of largest value	int which_max(vector x) { real max_x = max(x); int i = 0; while (x[i] != max_x) { i += 1; } return i; } which_max(v)

Derive

Map

Element-wise operations.

Action	Code	Details
Square elements	square(v)
Square root elements	sqrt(v)
Different multiplication per element	v .* w
Different power per element	exp(p * log(v))	only for strictly positive v
Different power per element	N = num_elements(v); vector c[N]; for (i in 1:N) { c[i] = v[i] ^ p[i]; }
Cumulative sum	cumulative_sum(v)
Softmax	softmax(v)
Log-softmax	log_softmax(v)
Dot product	v * w
Dot product (self)	dot_self(v)	v * v, or sum(v .* v)
Dot product	dot_product(v, w)

Grow

Action	Code	Details
Append element to column vector	append_row(v, x)
Prepend element to column vector	append_row(x, v)
Append element to row vector	append_col(v, x)
Prepend element to row vector	append_col(x, v)

Shrink

Action	Code	Details
First n elements (head)	head(v, n)
Last n elements (tail)	tail(v, n)
Slice	v[start:end]
Slice of length n	segment(v, start, n)

Reshape

Action	Code	Details
Transpose	v'

Convert

Action	Code	Details
To row vector	to_row_vector(v)
Transpose: from row to column vector, or vice versa	v'
To n by m matrix, column-major order	to_matrix(v, nrow, ncol)
To matrix with 1 row or column	to_matrix(v)	Depends on whether v is a row or column vector
To 1D array	to_array_1d(v)