I am working on database project in SWI-Prolog. Problem is that i want to work with names of Sportsmen which i read from input. I need to save their names with capital letters, but prolog interprets these as variables. Any ideas how to fix this?
I would use code_type/2 to ensure that any entered name starts with a capital letter.
Since you want to allow a user to enter a name with a letter that is either lower- or uppercase, I do the case conversion on the codes list that I read with read_line_to_codes/2.
Since you want to store the names in a database, I use dynamic/1 to declare that I will be adding some sportsname/1 entries, and I use assert/1 to add a specific name to the database.
Here is the code:
:- dynamic(sportsname/1).
:- initialization(input).
input:-
repeat,
format(user_output, 'Please enter a name (or type `quit`):\n', []),
read_line_to_codes(user_input, Codes1),
(
atom_codes(quit, Codes1)
->
!, true
;
capitalize(Codes1, Codes2)
->
atom_codes(Name, Codes2),
assert(sportsname(Name)),
format(current_output, 'Sportsname ~a writen to database.\n', [Name]),
fail
;
fail
).
capitalize([], []).
capitalize([H1|T], [H2|T]):-
code_type(H2, to_upper(H1)).
Example of use:
$ swipl sport_names.pl
Please enter a name (or type `quit`):
|: john
Sportsname John writen to database.
Please enter a name (or type `quit`):
|: James
Sportsname James writen to database.
Please enter a name (or type `quit`):
|: suzan
Sportsname Suzan writen to database.
Please enter a name (or type `quit`):
|: quit
?- sportsname(X).
X = 'John' ;
X = 'James' ;
X = 'Suzan'.
Hope this helps!
Use either quoted atoms...
?- atom('X').
true.
?- 'X' = 'Y'.
false.
... or strings:
?- X = "Foo!".
X = [70, 111, 111, 33].
(strings are represented as lists of codepoints, in this case ASCII ones). Quoted atoms are much easier to work with.
I don't know how implementation independent this code is, but this works for me in SWI-Prolog:
read_string(String) :-
current_input(Input),
read_line_to_codes(Input, Codes),
string_codes(String, Codes).
Sample input and output:
?- read_string(X).
|: Test!
X = "Test!".
Just quote any string that need to be read by Prolog, regardless to the case you find in the database... Beware to escaping: for instance
?- write('O\'Neal').
O'Neal
?- read(X).
|: 'O\'Neal'.
X = 'O\'Neal'.
Related
please assist with the following. i m trying to run a script that accepts one argument $1. The argument can either be a string or character or an integer. I want to use the argument in there where clause to search for the element in the database.
This is the table i want to search from:enter image description here
When i use the multiple conditions with OR , it works only when either the argument is a number or text.
This what my code looks like enter image description here
`
ELEMENT=$($PSQL "SELECT * FROM elements e FULL JOIN properties p USING(atomic_number) WHERE symbol = '$1' OR name = '$1' OR atomic_number = $1;")
`
and this is the results i get when i run with different aurgumentsenter image description here
Please help.
Thank you in advance
This will always fail on any non-numeric argument.
You are passing in H for hydrogen, but taking whatever was passed in and using it in the atomic_number comparison as an unquoted number, which the DB engine is trying to figure out what to do with. H isn't a number, and isn't a quoted string, so it must be the name of a column...but it isn't, so you are using invalid syntax.
I don't have a postgres available right now, but try something like this -
ELEMENT=$( $PSQL "
SELECT *
FROM elements e
FULL JOIN properties p USING(atomic_number)
WHERE symbol = '$1'
OR name = '$1'
OR atomic_number = CAST(`$1` as INTEGER); " )
Also, as an aside... avoid all-capital variable names.
As a convention, those are supposed to be system vars.
And please - please don't embed images except as helpful clarification.
Never rely on them to provide info if it can be avoided. Copy/paste actual formatted text people can copy/paste in their own testing.
An alternate way to construct the query: requires bash
looks_like_a_number() {
# only contains digits
[[ "$1" == +([[:digit:]]) ]]
}
sanitize() {
# at a minimum, handle embedded single quotes
printf '%s' "${1//\'/\'\'}"
}
if looks_like_a_number "$1"; then
field="atomic_number"
value=$1
elif [[ ${#1} -eq 1 ]]; then
field="symbol"
printf -v value "'%s'" "$(sanitize "$1")"
else
field="name"
printf -v value "'%s'" "$(sanitize "$1")"
fi
q="SELECT *
FROM elements e
FULL JOIN properties p USING(atomic_number)
WHERE $field = $value;"
printf '%s\n' "$q"
result=$("$PSQL" "$q")
I have a table:
h5file=open_file("ex.h5", "w")
class ex(IsDescription):
A=StringCol(5, pos=0)
B=StringCol(5, pos=1)
C=StringCol(5, pos=2)
table=h5file.create_table('/', 'table', ex, "Passing string as column name")
table=h5file.root.table
rows=[
('abc', 'bcd', 'dse'),
('der', 'fre', 'swr'),
('xsd', 'weq', 'rty')
]
table.append(rows)
table.flush()
I am trying to query as per below:
find='swr'
creteria='B'
if creteria=='B':
condition='B'
else:
condition='C'
value=[x['A'] for x in table.where("""condition==find""")]
print(value)
It returns:
ValueError: there are no columns taking part in condition condition==find
Is there a way to use condition as a column name in above query?
Thanks in advance.
Yes, you can use Pytables .where() to search based on a condition. The problem is how you constructed your query for the table.where(condition). See Note about strings under Table.where() in the Pytables Users Guide:
A special care should be taken when the query condition includes string literals. ... Python 3 strings are unicode objects.
in Python 3, “condition” should be defined like this:
condition = 'col1 == b"AAAA"'
The reason is that in Python 3 “condition” implies a comparison between a string of bytes (“col1” contents) and an unicode literal (“AAAA”).
The simplest form of your query is shown below. It returns a subset of rows that match the condition. Note use of single and double quotes for string and unicode:
query_table = table.where('C=="swr"') # search in column C
I rewrote your example as best I could. See below. It shows several ways to enter the condition. I'm not smart enough to figure out how to combine your creteria and find variables into a single condition variable with string and unicode characters.
from tables import *
class ex(IsDescription):
A=StringCol(5, pos=0)
B=StringCol(5, pos=1)
C=StringCol(5, pos=2)
h5file=open_file("ex.h5", "w")
table=h5file.create_table('/', 'table', ex, "Passing string as column name")
## table=h5file.root.table
rows=[
('abc', 'bcd', 'dse'),
('der', 'fre', 'swr'),
('xsd', 'weq', 'rty')
]
table.append(rows)
table.flush()
find='swr'
query_table = table.where('C==find')
for row in query_table :
print (row)
print (row['A'], row['B'], row['C'])
value=[x['A'] for x in table.where('C == "swr"')]
print(value)
value=[x['A'] for x in table.where('C == find')]
print(value)
h5file.close()
Output shown below:
/table.row (Row), pointing to row #1
b'der' b'fre' b'swr'
[b'der']
[b'der']
I'm trying to achieve the following behaviour with FsCheck: I'd like to create a generator that will generate a instance of MyUnion type, with every string field being non-null/empty.
type MyNestedUnion =
| X of string
| Y of int * string
type MyUnion =
| A of int * int * string * string
| B of MyNestedUnion
My 'real' type is much larger/deeper than the MyUnion, and FsCheck is able to generate a instance without any problem, but the string fields of the union cases are sometimes empty. (For example it might generate B (Y (123, "")))
Perhaps there's some obvious way of combining FsCheck's NonEmptyString and its support for generating arbitrary union types that I'm missing?
Any tips/pointers in the right direction greatly appreciated.
Thanks!
This goes against the grain of property based testing (in that you explicitly prevent valid test cases from being generated), but you could wire up the non-empty string generator to be used for all strings:
type Alt =
static member NonEmptyString () : Arbitrary<string> =
Arb.Default.NonEmptyString()
|> Arb.convert
(fun (nes : NonEmptyString) -> nes.Get)
NonEmptyString.NonEmptyString
Arb.register<Alt>()
let g = Arb.generate<MyUnion>
Gen.sample 1 10 g
Note that you'd need to re-register the default generator after the test since the mappings are global.
A more by-the-book solution would be to use the default derived generator and then filter values that contain invalid strings (i.e. use ==>), but you might find it not feasible for particularly deep nested types.
I'm using mksqlite to create and access an SQL database from matlab, and I want to get the number of rows in a table. I've tried this:
num = mksqlite('SELECT COUNT(*) FROM myTable');
, but the returned value isn't very helpful. If I put a breakpoint in my script and examine the variable, I find that it's a struct with a single field, called 'COUNT(_)', which seems to actually be an invalid name for a field, so I can't access it:
K>> class(num)
ans =
struct
K>> num
num =
COUNT(_): 0
K>> num.COUNT(_)
??? num.COUNT(_)
|
Error: The input character is not valid in MATLAB statements or expressions.
K>> num.COUNT()
??? Reference to non-existent field 'COUNT'.
K>> num.COUNT
??? Reference to non-existent field 'COUNT'.
Even the MATLAB IDE can't access it. If I try to double click the field in the variable editor, this gets spat out:
??? openvar('num.COUNT(_)', num.COUNT(_));
|
Error: The input character is not valid in MATLAB statements or expressions.
So how can I access this field?
You are correct that the problem is that mksqlite somehow manages to create an invalid field name that can't be read. The simplest solution is to add an AS clause to your SQL so that the field has a sensible name:
>> num = mksqlite('SELECT COUNT(*) AS cnt FROM myTable')
num =
cnt: 0
Then to remove the extra layer of indirection you can do:
>> num = num.cnt;
>> num
num =
0
SQLDF newbie here.
I have a data frame which has about 15,000 rows and 1 column.
The data looks like:
cars
autocar
carsinfo
whatisthat
donnadrive
car
telephone
...
I wanted to use the package sqldf to loop through the column and
pick all values which contain "car" anywhere in their value.
However, the following code generates an error.
> sqldf("SELECT Keyword FROM dat WHERE Keyword="car")
Error: unexpected symbol in "sqldf("SELECT Keyword FROM dat WHERE Keyword="car"
There is no unexpected symbol, so I'm not sure whats wrong.
so first, I want to know all the values which contain 'car'.
then I want to know only those values which contain just 'car' by itself.
Can anyone help.
EDIT:
allright, there was an unexpected symbol, but it only gives me just car and not every
row which contains 'car'.
> sqldf("SELECT Keyword FROM dat WHERE Keyword='car'")
Keyword
1 car
Using = will only return exact matches.
You should probably use the like operator combined with the wildcards % or _. The % wildcard will match multiple characters, while _ matches a single character.
Something like the following will find all instances of car, e.g. "cars", "motorcar", etc:
sqldf("SELECT Keyword FROM dat WHERE Keyword like '%car%'")
And the following will match "car" or "cars":
sqldf("SELECT Keyword FROM dat WHERE Keyword like 'car_'")
This has nothing to do with sqldf; your SQL statement is the problem. You need:
dat <- data.frame(Keyword=c("cars","autocar","carsinfo",
"whatisthat","donnadrive","car","telephone"))
sqldf("SELECT Keyword FROM dat WHERE Keyword like '%car%'")
# Keyword
# 1 cars
# 2 autocar
# 3 carsinfo
# 4 car
You can also use regular expressions to do this sort of filtering. grepl returns a logical vector (TRUE / FALSE) stating whether or not there was a match or not. You can get very sophisticated to match specific items, but a basic query will work in this case:
#Using #Joshua's dat data.frame
subset(dat, grepl("car", Keyword, ignore.case = TRUE))
Keyword
1 cars
2 autocar
3 carsinfo
6 car
Very similar to the solution provided by #Chase. Because we do not use subset we do not need a logical vector and can use both grep or grepl:
df <- data.frame(keyword = c("cars", "autocar", "carsinfo", "whatisthat", "donnadrive", "car", "telephone"))
df[grep("car", df$keyword), , drop = FALSE] # or
df[grepl("car", df$keyword), , drop = FALSE]
keyword
1 cars
2 autocar
3 carsinfo
6 car
I took the idea from Selecting rows where a column has a string like 'hsa..' (partial string match)