Expression API

DataFrame methods such as select and filter accept one or more logical expressions and there are many functions available for creating logical expressions. These are documented below.

Tip

Most functions and methods may receive and return an Expr, which can be chained together using a fluent-style API:

use datafusion::prelude::*;
// create the expression `(a > 6) AND (b < 7)`
col("a").gt(lit(6)).and(col("b").lt(lit(7)));

Identifiers

Syntax	Description
col(ident)	Reference a column in a dataframe col("a")

Note

ident

A type which implement Into<Column> trait

Literal Values

Syntax	Description
lit(value)	Literal value such as lit(123) or lit("hello")

Note

value

A type which implement Literal

Boolean Expressions

Syntax	Description
and(x, y), x.and(y)	Logical AND
or(x, y), x.or(y)	Logical OR
!x, not(x), x.not()	Logical NOT

Note

! is a bitwise or logical complement operator in Rust, but it only works as a logical NOT in expression API.

Note

Since && and || are logical operators in Rust and cannot be overloaded these are not available in the expression API.

Bitwise Expressions

Syntax	Description
x & y, bitwise_and(x, y), x.bitand(y)	AND
x | y, bitwise_or(x, y), x.bitor(y)	OR
x ^ y, bitwise_xor(x, y), x.bitxor(y)	XOR
x << y, bitwise_shift_left(x, y), x.shl(y)	Left shift
x >> y, bitwise_shift_right(x, y), x.shr(y)	Right shift

Comparison Expressions

Syntax	Description
x.eq(y)	Equal
x.not_eq(y)	Not Equal
x.gt(y)	Greater Than
x.gt_eq(y)	Greater Than or Equal
x.lt(y)	Less Than
x.lt_eq(y)	Less Than or Equal

Note

Comparison operators (<, <=, ==, >=, >) could be overloaded by the PartialOrd and PartialEq trait in Rust, but these operators always return a bool which makes them not work with the expression API.

Arithmetic Expressions

Syntax	Description
x + y, x.add(y)	Addition
x - y, x.sub(y)	Subtraction
x * y, x.mul(y)	Multiplication
x / y, x.div(y)	Division
x % y, x.rem(y)	Remainder
-x, x.neg()	Negation

Math Functions

Syntax	Description
abs(x)	absolute value
acos(x)	inverse cosine
acosh(x)	inverse hyperbolic cosine
asin(x)	inverse sine
asinh(x)	inverse hyperbolic sine
atan(x)	inverse tangent
atanh(x)	inverse hyperbolic tangent
atan2(y, x)	inverse tangent of y / x
cbrt(x)	cube root
ceil(x)	nearest integer greater than or equal to argument
cos(x)	cosine
cosh(x)	hyperbolic cosine
degrees(x)	converts radians to degrees
exp(x)	exponential
factorial(x)	factorial
floor(x)	nearest integer less than or equal to argument
gcd(x, y)	greatest common divisor
isnan(x)	predicate determining whether NaN/-NaN or not
iszero(x)	predicate determining whether 0.0/-0.0 or not
lcm(x, y)	least common multiple
ln(x)	natural logarithm
log(base, x)	logarithm of x for a particular base
log10(x)	base 10 logarithm
log2(x)	base 2 logarithm
nanvl(x, y)	returns x if x is not NaN otherwise returns y
pi()	approximate value of π
power(base, exponent)	base raised to the power of exponent
radians(x)	converts degrees to radians
round(x)	round to nearest integer
signum(x)	sign of the argument (-1, 0, +1)
sin(x)	sine
sinh(x)	hyperbolic sine
sqrt(x)	square root
tan(x)	tangent
tanh(x)	hyperbolic tangent
trunc(x)	truncate toward zero

Note

Unlike to some databases the math functions in Datafusion works the same way as Rust math functions, avoiding failing on corner cases e.g.

select log(-1), log(0), sqrt(-1);
+----------------+---------------+-----------------+
| log(Int64(-1)) | log(Int64(0)) | sqrt(Int64(-1)) |
+----------------+---------------+-----------------+
| NaN            | -inf          | NaN             |
+----------------+---------------+-----------------+

Conditional Expressions

Syntax	Description
coalesce([value, …])	Returns the first of its arguments that is not null. Null is returned only if all arguments are null. It is often used to substitute a default value for null values when data is retrieved for display.
case(expr)     .when(expr)     .end(), case(expr)     .when(expr)     .otherwise(expr)	CASE expression. The expression may chain multiple when expressions and end with an end or otherwise expression. Example: case(col(“a”) % lit(3))     .when(lit(0), lit(“A”))     .when(lit(1), lit(“B”))     .when(lit(2), lit(“C”))     .end() or, end with otherwise to match any other conditions: case(col(“b”).gt(lit(100)))     .when(lit(true), lit(“value > 100”))     .otherwise(lit(“value <= 100”))
nullif(value1, value2)	Returns a null value if value1 equals value2; otherwise it returns value1. This can be used to perform the inverse operation of the coalesce expression.

String Expressions

Syntax	Description
ascii(character)	Returns a numeric representation of the character (character). Example: ascii('a') -> 97
bit_length(text)	Returns the length of the string (text) in bits. Example: bit_length('spider') -> 48
btrim(text, characters)	Removes all specified characters (characters) from both the beginning and the end of the string (text). Example: btrim('aabchelloccb', 'abc') -> hello
char_length(text)	Returns number of characters in the string (text). The same as character_length and length. Example: character_length('lion') -> 4
character_length(text)	Returns number of characters in the string (text). The same as char_length and length. Example: char_length('lion') -> 4
concat(value1, [value2 [, …]])	Concatenates the text representations (value1, [value2 [, ...]]) of all the arguments. NULL arguments are ignored. Example: concat('aaa', 'bbc', NULL, 321) -> aaabbc321
concat_ws(separator, value1, [value2 [, …]])	Concatenates the text representations (value1, [value2 [, ...]]) of all the arguments with the separator (separator). NULL arguments are ignored. concat_ws('/', 'path', 'to', NULL, 'my', 'folder', 123) -> path/to/my/folder/123
chr(integer)	Returns a character by its numeric representation (integer). Example: chr(90) -> 8
initcap	Converts the first letter of each word to upper case and the rest to lower case. Example: initcap('hi TOM') -> Hi Tom
left(text, number)	Returns a certain number (number) of first characters (text). Example: left('like', 2) -> li
length(text)	Returns number of characters in the string (text). The same as character_length and char_length. Example: length('lion') -> 4
lower(text)	Converts all characters in the string (text) into lower case. Example: lower('HELLO') -> hello
lpad(text, length, [, fill])	Extends the string to length (length) by prepending the characters (fill) (a space by default). Example: lpad('bb', 5, 'a') → aaabb
ltrim(text, text)	Removes all specified characters (characters) from the beginning of the string (text). Example: ltrim('aabchelloccb', 'abc') -> helloccb
md5(text)	Computes the MD5 hash of the argument (text).
octet_length(text)	Returns number of bytes in the string (text).
repeat(text, number)	Repeats the string the specified number of times. Example: repeat('1', 4) -> 1111
replace(string, from, to)	Replaces a specified string (from) with another specified string (to) in the string (string). Example: replace('Hello', 'replace', 'el') -> Hola
reverse(text)	Reverses the order of the characters in the string (text). Example: reverse('hello') -> olleh
right(text, number)	Returns a certain number (number) of last characters (text). Example: right('like', 2) -> ke
rpad(text, length, [, fill])	Extends the string to length (length) by prepending the characters (fill) (a space by default). Example: rpad('bb', 5, 'a') → bbaaa
rtrim	Removes all specified characters (characters) from the end of the string (text). Example: rtrim('aabchelloccb', 'abc') -> aabchello
digest(input, algorithm)	Computes the binary hash of input, using the algorithm.
split_part(string, delimiter, index)	Splits the string (string) based on a delimiter (delimiter) and picks out the desired field based on the index (index).
starts_with(string, prefix)	Returns true if the string (string) starts with the specified prefix (prefix). If not, it returns false. Example: starts_with('Hi Tom', 'Hi') -> true
strpos	Finds the position from where the substring matches the string
substr(string, position, [, length])	Returns substring from the position (position) with length (length) characters in the string (string).
translate(string, from, to)	Replaces the characters in from with the counterpart in to. Example: translate('abcde', 'acd', '15') -> 1b5e
trim(string)	Removes all characters, space by default from the string (string)
upper	Converts all characters in the string into upper case. Example: upper('hello') -> HELLO

Array Expressions

Syntax	Description
array_any_value(array)	Returns the first non-null element in the array. array_any_value([NULL, 1, 2, 3]) -> 1
array_append(array, element)	Appends an element to the end of an array. array_append([1, 2, 3], 4) -> [1, 2, 3, 4]
array_concat(array[, …, array_n])	Concatenates arrays. array_concat([1, 2, 3], [4, 5, 6]) -> [1, 2, 3, 4, 5, 6]
array_has(array, element)	Returns true if the array contains the element array_has([1,2,3], 1) -> true
array_has_all(array, sub-array)	Returns true if all elements of sub-array exist in array array_has_all([1,2,3], [1,3]) -> true
array_has_any(array, sub-array)	Returns true if any elements exist in both arrays array_has_any([1,2,3], [1,4]) -> true
array_dims(array)	Returns an array of the array’s dimensions. array_dims([[1, 2, 3], [4, 5, 6]]) -> [2, 3]
array_distinct(array)	Returns distinct values from the array after removing duplicates. array_distinct([1, 3, 2, 3, 1, 2, 4]) -> [1, 2, 3, 4]
array_element(array, index)	Extracts the element with the index n from the array array_element([1, 2, 3, 4], 3) -> 3
empty(array)	Returns true for an empty array or false for a non-empty array. empty([1]) -> false
flatten(array)	Converts an array of arrays to a flat array flatten([[1], [2, 3], [4, 5, 6]]) -> [1, 2, 3, 4, 5, 6]
array_length(array, dimension)	Returns the length of the array dimension. array_length([1, 2, 3, 4, 5]) -> 5
array_ndims(array)	Returns the number of dimensions of the array. array_ndims([[1, 2, 3], [4, 5, 6]]) -> 2
array_pop_front(array)	Returns the array without the first element. array_pop_front([1, 2, 3]) -> [2, 3]
array_pop_back(array)	Returns the array without the last element. array_pop_back([1, 2, 3]) -> [1, 2]
array_position(array, element)	Searches for an element in the array, returns first occurrence. array_position([1, 2, 2, 3, 4], 2) -> 2
array_positions(array, element)	Searches for an element in the array, returns all occurrences. array_positions([1, 2, 2, 3, 4], 2) -> [2, 3]
array_prepend(array, element)	Prepends an element to the beginning of an array. array_prepend(1, [2, 3, 4]) -> [1, 2, 3, 4]
array_repeat(element, count)	Returns an array containing element count times. array_repeat(1, 3) -> [1, 1, 1]
array_remove(array, element)	Removes the first element from the array equal to the given value. array_remove([1, 2, 2, 3, 2, 1, 4], 2) -> [1, 2, 3, 2, 1, 4]
array_remove_n(array, element, max)	Removes the first max elements from the array equal to the given value. array_remove_n([1, 2, 2, 3, 2, 1, 4], 2, 2) -> [1, 3, 2, 1, 4]
array_remove_all(array, element)	Removes all elements from the array equal to the given value. array_remove_all([1, 2, 2, 3, 2, 1, 4], 2) -> [1, 3, 1, 4]
array_replace(array, from, to)	Replaces the first occurrence of the specified element with another specified element. array_replace([1, 2, 2, 3, 2, 1, 4], 2, 5) -> [1, 5, 2, 3, 2, 1, 4]
array_replace_n(array, from, to, max)	Replaces the first max occurrences of the specified element with another specified element. array_replace_n([1, 2, 2, 3, 2, 1, 4], 2, 5, 2) -> [1, 5, 5, 3, 2, 1, 4]
array_replace_all(array, from, to)	Replaces all occurrences of the specified element with another specified element. array_replace_all([1, 2, 2, 3, 2, 1, 4], 2, 5) -> [1, 5, 5, 3, 5, 1, 4]
array_slice(array, begin,end)	Returns a slice of the array. array_slice([1, 2, 3, 4, 5, 6, 7, 8], 3, 6) -> [3, 4, 5, 6]
array_slice(array, begin, end, stride)	Returns a slice of the array with added stride feature. array_slice([1, 2, 3, 4, 5, 6, 7, 8], 3, 6, 2) -> [3, 5, 6]
array_to_string(array, delimiter)	Converts each element to its text representation. array_to_string([1, 2, 3, 4], ',') -> 1,2,3,4
array_intersect(array1, array2)	Returns an array of the elements in the intersection of array1 and array2. array_intersect([1, 2, 3, 4], [5, 6, 3, 4]) -> [3, 4]
array_union(array1, array2)	Returns an array of the elements in the union of array1 and array2 without duplicates. array_union([1, 2, 3, 4], [5, 6, 3, 4]) -> [1, 2, 3, 4, 5, 6]
array_except(array1, array2)	Returns an array of the elements that appear in the first array but not in the second. array_except([1, 2, 3, 4], [5, 6, 3, 4]) -> [1, 2]
array_resize(array, size, value)	Resizes the list to contain size elements. Initializes new elements with value or empty if value is not set. array_resize([1, 2, 3], 5, 0) -> [1, 2, 3, 0, 0]
array_sort(array, desc, null_first)	Returns sorted array. array_sort([3, 1, 2, 5, 4]) -> [1, 2, 3, 4, 5]
cardinality(array/map)	Returns the total number of elements in the array or map. cardinality([[1, 2, 3], [4, 5, 6]]) -> 6
make_array(value1, [value2 [, …]])	Returns an Arrow array using the specified input expressions. make_array(1, 2, 3) -> [1, 2, 3]
range(start [, stop, step])	Returns an Arrow array between start and stop with step. SELECT range(2, 10, 3) -> [2, 5, 8]
string_to_array(array, delimiter, null_string)	Splits a string based on a delimiter and returns an array of parts. Any parts matching the optional null_string will be replaced with NULL. string_to_array('abc#def#ghi', '#', ' ') -> ['abc', 'def', 'ghi']
trim_array(array, n)	Deprecated

Regular Expressions

Syntax	Description
regexp_match	Matches a regular expression against a string and returns matched substrings.
regexp_replace	Replaces strings that match a regular expression

Temporal Expressions

Syntax	Description
date_part	Extracts a subfield from the date.
date_trunc	Truncates the date to a specified level of precision.
from_unixtime	Returns the unix time in format.
to_timestamp	Converts a string to a Timestamp(_, _)
to_timestamp_millis	Converts a string to a Timestamp(Milliseconds, None)
to_timestamp_micros	Converts a string to a Timestamp(Microseconds, None)
to_timestamp_seconds	Converts a string to a Timestamp(Seconds, None)
now()	Returns current time.

Other Expressions

Syntax	Description
array([value1, …])	Returns an array of fixed size with each argument ([value1, ...]) on it.
in_list(expr, list, negated)	Returns true if (expr) belongs or not belongs (negated) to a list (list), otherwise returns false.
random()	Returns a random value from 0 (inclusive) to 1 (exclusive).
sha224(text)	Computes the SHA224 hash of the argument (text).
sha256(text)	Computes the SHA256 hash of the argument (text).
sha384(text)	Computes the SHA384 hash of the argument (text).
sha512(text)	Computes the SHA512 hash of the argument (text).
to_hex(integer)	Converts the integer (integer) to the corresponding hexadecimal string.

Aggregate Functions

Syntax	Description
avg(expr)	Сalculates the average value for expr.
approx_distinct(expr)	Calculates an approximate count of the number of distinct values for expr.
approx_median(expr)	Calculates an approximation of the median for expr.
approx_percentile_cont(expr, percentile)	Calculates an approximation of the specified percentile for expr.
approx_percentile_cont_with_weight(expr, weight_expr, percentile)	Calculates an approximation of the specified percentile for expr and weight_expr.
bit_and(expr)	Computes the bitwise AND of all non-null input values for expr.
bit_or(expr)	Computes the bitwise OR of all non-null input values for expr.
bit_xor(expr)	Computes the bitwise exclusive OR of all non-null input values for expr.
bool_and(expr)	Returns true if all non-null input values (expr) are true, otherwise false.
bool_or(expr)	Returns true if any non-null input value (expr) is true, otherwise false.
count(expr)	Returns the number of rows for expr.
count_distinct	Creates an expression to represent the count(distinct) aggregate function
cube(exprs)	Creates a grouping set for all combination of exprs
grouping_set(exprs)	Create a grouping set.
max(expr)	Finds the maximum value of expr.
median(expr)	Сalculates the median of expr.
min(expr)	Finds the minimum value of expr.
rollup(exprs)	Creates a grouping set for rollup sets.
sum(expr)	Сalculates the sum of expr.

Aggregate Function Builder

You can also use the ExprFunctionExt trait to more easily build Aggregate arguments Expr.

See datafusion-examples/examples/expr_api.rs for example usage.

Syntax	Equivalent to
first_value_udaf.call(vec![expr]).order_by(vec![expr]).build().unwrap()	first_value(expr, Some(vec![expr]))

Subquery Expressions

Syntax	Description
exists	Creates an EXISTS subquery expression
in_subquery	df1.filter(in_subquery(col("foo"), df2))? is the equivalent of the SQL WHERE foo IN <df2>
not_exists	Creates a NOT EXISTS subquery expression
not_in_subquery	Creates a NOT IN subquery expression
scalar_subquery	Creates a scalar subquery expression

User-Defined Function Expressions

Syntax	Description
create_udf	Creates a new UDF with a specific signature and specific return type.
create_udaf	Creates a new UDAF with a specific signature, state type and return type.

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