NULL

Instance of:

AKA: null, NULL

Distinct from:

English:

Formalization:

\[ \]

Cites: Wikipedia Null (SQL)) ; Wikidata Q371029

R null values: NULL, NA, NaN, Inf

Code

Imports and spin up toy data objects and databases. 
toy_vector_numeric <- c(1,2,3,4,5)
toy_vector_character <- c('a','b','c','d','e')
toy_matrix <- matrix(1:9, nrow=3,ncol=3)
toy_list <- list('a','1',T,c('red','green'))
toy_df <- data.frame(id=c('unit1','unit2','unit3'), y=c(1,2,3), x= c(3,2,1))

toy_dirty_df <- data.frame(id=c('','NA','NaN','inf'), y=c(1,2,3,4), x= c(0,NA,NaN,Inf)) #can't explicitly include NULL 

library(data.table)
toy_dt <- data.table(id=c('unit1','unit2','unit3'), y=c(1,2,3), x= c(3,2,1))
toy_dirty_dt <- as.data.table(toy_dirty_df)
library(tidyverse)
── Attaching packages ─────────────────────────────────────── tidyverse 1.3.2 ──
✔ ggplot2 3.4.0      ✔ purrr   0.3.5 
✔ tibble  3.1.8      ✔ dplyr   1.0.10
✔ tidyr   1.2.1      ✔ stringr 1.5.0 
✔ readr   2.1.3      ✔ forcats 0.5.2 
── Conflicts ────────────────────────────────────────── tidyverse_conflicts() ──
✖ dplyr::between()   masks data.table::between()
✖ dplyr::filter()    masks stats::filter()
✖ dplyr::first()     masks data.table::first()
✖ dplyr::lag()       masks stats::lag()
✖ dplyr::last()      masks data.table::last()
✖ purrr::transpose() masks data.table::transpose()
library(arrow)

Attaching package: 'arrow'

The following object is masked from 'package:utils':

    timestamp
import numpy as np
toy_vector_numeric = np.array([1,2,3,4,5])
toy_vector_character = np.array(['a','b','c','d','e'])
toy_list = ['a','1',True,['red','green']]
toy_dictionary = { 'a':1 , 'b':2, 'c':3}

from jax import numpy as jnp
toy_vector_numeric_jax = jnp.array([1,2,3,4,5])
#toy_vector_character_jax = jnp.array(['a','b','c','d','e']) #only numeric is allowed in jax
WARNING:jax._src.lib.xla_bridge:No GPU/TPU found, falling back to CPU. (Set TF_CPP_MIN_LOG_LEVEL=0 and rerun for more info.)
import pandas as pd
toy_df = pd.DataFrame(data={'id': ['unit1','unit2','unit3'], 'y': [1, 2, 3], 'x': [3, 2, 1]})

import torch

import tensorflow as tf

import pyarrow as pa
library(DBI)
# Create an ephemeral in-memory RSQLite database
#con <- dbConnect(RSQLite::SQLite(), dbname = ":memory:")
#dbListTables(con)
#dbWriteTable(con, "mtcars", mtcars)
#dbListTables(con)

#Configuration failed because libpq was not found. Try installing:
#* deb: libpq-dev libssl-dev (Debian, Ubuntu, etc)
#install.packages('RPostgres')
#remotes::install_github("r-dbi/RPostgres")
#Took forever because my file permissions were broken
#pg_lsclusters
require(RPostgres)
# Connect to the default postgres database
#I had to follow these instructions and create both a username and database that matched my ubuntu name
#https://www.digitalocean.com/community/tutorials/how-to-install-postgresql-on-ubuntu-20-04-quickstart
con_Postgres <- dbConnect(RPostgres::Postgres())

DROP TABLE IF EXISTS toy_df;

CREATE TABLE IF NOT EXISTS toy_df (
  id varchar(5),
    y INTEGER,
    x INTEGER
);

INSERT INTO toy_df (id, y, x)
VALUES
    ('unit1',1,3),
    ('unit2',2,2),
    ('unit3',3,1);
    
#install.packages("duckdb")
library("DBI")
con_duckdb = dbConnect(duckdb::duckdb(), ":memory:")
#pip install duckdb==0.6.0
import duckdb
con_duckdb = duckdb.connect()

0.1 R

Base

The Null Object

class(NULL)
[1] "NULL"
is.null(NULL)
[1] TRUE
length(NULL)
[1] 0
is.null(list())     # FALSE (on purpose!)
[1] FALSE
is.null(pairlist()) # TRUE
[1] TRUE
is.null(integer(0)) # FALSE
[1] FALSE
is.null(logical(0)) # FALSE
[1] FALSE
as.null(list(a = 1, b = "c"))
NULL

Tidyverse

Is object an empty vector or NULL?

is_empty(NULL)
[1] TRUE
is_empty(list())
[1] TRUE
is_empty(list(NULL))
[1] FALSE
NULL==NA
logical(0)
NULL==6
logical(0)

Default value for NULL

#Replace Nulls
1 %||% 2
[1] 1
NULL %||% 2
[1] 2

DataTable

Arrow

Apache Arrow data types “These functions create type objects corresponding to Arrow types. Use them when defining a schema() or as inputs to other types, like struct. Most of these functions don’t take arguments, but a few do.”

null()
Null
null

0.2 Python

0.2.0.1 3.x / math/ statistics

None Python None Keyword

None An object frequently used to represent the absence of a value, as when default arguments are not passed to a function. Assignments to None are illegal and raise a SyntaxError. None is the sole instance of the NoneType type.


type(None)
<class 'NoneType'>
None is True
False
None is False
False
try:
    print(len(None))
except Exception as ex:
    print(ex)
    
object of type 'NoneType' has no len()

try:
    print(len(None)) #None has no length
except Exception as ex:
    print(ex)
object of type 'NoneType' has no len()

0.2.0.2 NumPy / SciPy / scikit-learn


np.array([[ None,  None],
          [ None,  None]])
array([[None, None],
       [None, None]], dtype=object)
np.array([[ None,  None],
          [ None,  None]], dtype=bool)
          
array([[False, False],
       [False, False]])

0.2.0.3 Pandas


pd.Series([None, None])
0    None
1    None
dtype: object
pd.Series([None, None]).isnull()
0    True
1    True
dtype: bool
pd.Series([1, None]).notnull()
0     True
1    False
dtype: bool

0.3 Jax


jnp.array([[ None,  None],
           [ None,  None]])
           
DeviceArray([[nan, nan],
             [nan, nan]], dtype=float32)

0.4 Numpyro

Uses jax’s boolean array

0.5 Stan

0.6 Torch

TORCH.NAN_TO_NUM


torch.tensor([float('nan'), float('inf'), -float('inf'), 3.14])
tensor([   nan,    inf,   -inf, 3.1400])
try:
    print(torch.tensor([None])) #Fails
except Exception as ex:
    print(ex)
    
Could not infer dtype of NoneType

0.7 Tensorflow


tf.constant([5.0, np.nan, 6.8, np.nan, np.inf])
<tf.Tensor: shape=(5,), dtype=float32, numpy=array([5. , nan, 6.8, nan, inf], dtype=float32)>
tf.math.is_nan(tf.constant([5.0, np.nan, 6.8, np.nan, np.inf]))
<tf.Tensor: shape=(5,), dtype=bool, numpy=array([False,  True, False,  True, False])>
try:
    print(tf.constant([None,None], dtype=tf.bool))
except Exception as ex:
    print(ex)
Attempt to convert a value (None) with an unsupported type (<class 'NoneType'>) to a Tensor.

0.8 PostgreSQL


DROP TABLE IF EXISTS null_df;

CREATE TABLE IF NOT EXISTS null_df (
  example_null boolean,
  example_notnull boolean NOT NULL
);

Error: Failed to fetch row: ERROR: null value in column “example_notnull” of relation “null_df” violates not-null constraint DETAIL: Failing row contains (t, null).


INSERT INTO null_df (example_null, example_notnull)
VALUES
  (NULL, False),
  (TRUE, NULL);
;

INSERT INTO null_df (example_null, example_notnull)
VALUES
  (NULL, False),
  (TRUE, TRUE);
;

SELECT * from null_df;
0 records
example_null example_notnull

0.9 DuckDB

Boolean Type


DROP TABLE IF EXISTS null_df;

CREATE TABLE IF NOT EXISTS null_df (
  example_null boolean,
  example_notnull boolean NOT NULL
);

Error: rapi_execute: Failed to run query Error: Constraint Error: NOT NULL constraint failed: null_df.example_notnull Failed to execute SQL chunk


INSERT INTO null_df (example_null, example_notnull)
VALUES
  (NULL, False),
  (TRUE, NULL);
;

INSERT INTO null_df (example_null, example_notnull)
VALUES
  (NULL, False),
  (TRUE, TRUE);
;

SELECT * from null_df;
0 records
example_null example_notnull