str.split = split(self, /, sep=None, maxsplit=-1)
Return a list of the words in the string, using sep as the delimiter string.
sep
The delimiter according which to split the string.
None (the default value) means split according to any whitespace,
and discard empty strings from the result.
maxsplit
Maximum number of splits to do.
-1 (the default value) means no limit.
The /, which would seem to be a 2nd argument is a new notation to me. What is it doing there?
From What's New in Python 3.8:
Positional-only parameters
There is a new function parameter syntax / to indicate that some function parameters must be specified positionally and cannot be used as keyword arguments.
In the following example, parameters a and b are positional-only, while c or d can be positional or keyword, and e or f are required to be keywords:
def f(a, b, /, c, d, *, e, f):
print(a, b, c, d, e, f)
One use case for this notation is that it allows pure Python functions to fully emulate behaviors of existing C coded functions.
Related
I am trying to separate my String using spaces and extract the second text of the String value.
Here is my code -
String title = 'testing abcdefgh.abc.cde.fgh test testing issue'
String[] test = title.split(" ");
String[] newTest = test[1];
println newTest
Here is the output i am getting - [a, b, c, d, ., a, b, c, ., c, d, e, ., f, g, h]
NOw the output i am looking for is abcd.abc.cde.fgh, but i am getting [a, b, c, d, ., a, b, c, ., c, d, e, ., f, g, h]
I have used ("\s+"), ("\s"), just a space inside brackets, single and double quotes enclosing a space, nothing works.
It's because here
String[] newTest = test[1]
You tell groovy to stick the string you want into a string array
So groovy tries to do what you say, and splits the characters out into separate strings
What you want is just a string, not a string array. Try
String newTest = test[1]
Instead
I think the problem is that in Java you have to escape a backslash in a String literal. So while the pattern you want is \s+, you have to put this in Java as "\\s+"
I would like to have a procedure which makes a local copy b of input character a (of not assumed length) into an allocatable array of characters. I do have the following code
program test_copystr
character(len=6) :: str
str = 'abc'
call copystr(str)
contains
subroutine copystr(a)
character(len=*), intent(in) :: a
!> Local variables
integer :: i
character, allocatable :: b(:)
allocate(b(len_trim(a)))
do i=1, len_trim(a)
b(i) = a(i:i)
end do
print *, b
b(1:len_trim(a)) = a(1:len_trim(a))
print *, b
end subroutine copystr
end program test_copystr
where I'm trying to assign a to b in two different ways. The result is
abc
aaa
I thought that both assignments should yield the same output. Can anyone explain me that difference? (To compile this code I'm using gfortran 5.2.0 compiler.)
As you know b is an array of characters while a is a scalar; when the subroutine is called it is a 6-character string. These are different things. The statement
b(1:len_trim(a)) = a(1:len_trim(a))
specifies the array section b(1:3) on the lhs, that is all 3 elements of b, and the substring a(1:3) on the rhs. Now, when assigning a substring of length 3 to a single character such as any element of b Fortran assigns only the first character of the string.
In this case every element of b is set to the first character of a. It is as if the compiler generates the 3 statements
b(1) = 'abc'
b(2) = 'abc'
b(3) = 'abc'
to implement the array assignment. This is what Fortran's array syntax does with an array on the lhs and a scalar (expression) on the rhs, it broadcasts the scalar to each element of the array.
The first method you use, looping across the elements of b and the characters of a is the regular way make an array of characters equivalent to a string. But you could try transfer -- see my answer to this question Removing whitespace in string
Is it possible to substitute characters according to a list in Lua, like tr in Perl? For example, I would like to substitute A to B and B to A (e.g. AABBCC becomes BBAACC).
In Perl, the solution would be $str ~= tr/AB/BA/. Is there any native way of doing this in Lua? If not, I think the best solution would be iterating through the entire string, since separate substitutions need to use a special symbol to distinguish characters that were already substituted and characters that weren't.
Edit: my goal was to calculate the reverse complement of a DNA string, as described here.
string.gsub can take a table as the third argument. The table is queried for each match, using the first capture as the key, and the associated value is used as the replacement string. If the value is nil, the match is not changed.
So you can build a helper table like this:
local s = "AABBCC"
local t = {A = "B", B = "A"}
local result = string.gsub(s, "[AB]", t)
print(result)
or this same one-liner:
print((string.gsub("AABBCC", "[AB]", {A = "B", B = "A"})))
Output:
BBAACC
For a one character pattern like "[AB]", "." can work as well because whatever not found in the table won't be changed. (But I don't think that's more efficient) But for some more complicated cases, a good pattern is needed.
Here is an example from Programming in Lua: this function substitutes the value of the global variable varname for every occurrence of $varname in a string:
function expand (s)
return (string.gsub(s, "$(%w+)", _G))
end
The code below will replace each character with a desired mapping (or leave alone if no mapping exists). You could modify the second parameter to string.gsub in tr to be more specific if you know the exact range of characters.
s = "AABBCC"
mappings = {["A"]="B",["B"]="A"}
function tr(s,mappings)
return string.gsub(s,
"(.)",
function(m)
-- print("found",m,"replace with",mappings[m],mappings[m] or m)
if mappings[m] == nil then return m else return mappings[m] end
end
)
end
print(tr(s,mappings))
Outputs
henry#henry-pc:~/Desktop$ lua replace.lua
found A replace with B B
found A replace with B B
found B replace with A A
found B replace with A A
found C replace with nil C
found C replace with nil C
BBAACC 6
Following is my REPL output. I am not sure why string.split does not work here.
val s = "Pedro|groceries|apple|1.42"
s: java.lang.String = Pedro|groceries|apple|1.42
scala> s.split("|")
res27: Array[java.lang.String] = Array("", P, e, d, r, o, |, g, r, o, c, e, r, i, e, s, |, a, p, p, l, e, |, 1, ., 4, 2)
If you use quotes, you're asking for a regular expression split. | is the "or" character, so your regex matches nothing or nothing. So everything is split.
If you use split('|') or split("""\|""") you should get what you want.
| is a special regular expression character which is used as a logical operator for OR operations.
Since java.lang.String#split(String regex); takes in a regular expression, you're splitting the string with "none OR none", which is a whole another speciality about regular expression splitting, where none essentially means "between every single character".
To get what you want, you need to escape your regex pattern properly. To escape the pattern, you need to prepend the character with \ and since \ is a special String character (think \t and \r for example), you need to actually double escape so that you'll end up with s.split("\\|").
For full Java regular expression syntax, see java.util.regex.Pattern javadoc.
Split takes a regex as first argument, so your call is interpreted as "empty string or empty string". To get the expected behavior you need to escape the pipe character "\\|".
I'm trying to write a simple function that takes two inputs, x and y, and passes these to three other simple functions that add, multiply, and divide them. The main function should then display the results as a string containing x, y, and the totals.
I think there's something I'm not understanding about output arguments. Anyway, here's my (pitiful) code:
function a=addxy(x,y)
a=x+y;
function b=mxy(x,y)
b=x*y;
function c=dxy(x,y)
c=x/y;
The main function is:
function [d e f]=answer(x,y)
d=addxy(x,y);
e=mxy(x,y);
f=dxy(x,y);
z=[d e f]
How do I get the values for x, y, d, e, and f into a string? I tried different matrices and stuff like:
['the sum of' x 'and' y 'is' d]
but none of the variables are showing up.
Two additional issues:
Why is the function returning "ans 3" even though I didn't ask for the length of z?
If anyone could recommend a good book for beginners to MATLAB scripting I'd really appreciate it.
Here's how you convert numbers to strings, and join strings to other things (it's weird):
>> ['the number is ' num2str(15) '.']
ans =
the number is 15.
You can use fprintf/sprintf with familiar C syntax. Maybe something like:
fprintf('x = %d, y = %d \n x+y=%d \n x*y=%d \n x/y=%f\n', x,y,d,e,f)
reading your comment, this is how you use your functions from the main program:
x = 2;
y = 2;
[d e f] = answer(x,y);
fprintf('%d + %d = %d\n', x,y,d)
fprintf('%d * %d = %d\n', x,y,e)
fprintf('%d / %d = %f\n', x,y,f)
Also for the answer() function, you can assign the output values to a vector instead of three distinct variables:
function result=answer(x,y)
result(1)=addxy(x,y);
result(2)=mxy(x,y);
result(3)=dxy(x,y);
and call it simply as:
out = answer(x,y);
As Peter and Amro illustrate, you have to convert numeric values to formatted strings first in order to display them or concatenate them with other character strings. You can do this using the functions FPRINTF, SPRINTF, NUM2STR, and INT2STR.
With respect to getting ans = 3 as an output, it is probably because you are not assigning the output from answer to a variable. If you want to get all of the output values, you will have to call answer in the following way:
[out1,out2,out3] = answer(1,2);
This will place the value d in out1, the value e in out2, and the value f in out3. When you do the following:
answer(1,2)
MATLAB will automatically assign the first output d (which has the value 3 in this case) to the default workspace variable ans.
With respect to suggesting a good resource for learning MATLAB, you shouldn't underestimate the value of the MATLAB documentation. I've learned most of what I know on my own using it. You can access it online, or within your copy of MATLAB using the functions DOC, HELP, or HELPWIN.
I just realized why I was having so much trouble - in MATLAB you can't store strings of different lengths as an array using square brackets. Using square brackets concatenates strings of varying lengths into a single character array.
>> a=['matlab','is','fun']
a =
matlabisfun
>> size(a)
ans =
1 11
In a character array, each character in a string counts as one element, which explains why the size of a is 1X11.
To store strings of varying lengths as elements of an array, you need to use curly braces to save as a cell array. In cell arrays, each string is treated as a separate element, regardless of length.
>> a={'matlab','is','fun'}
a =
'matlab' 'is' 'fun'
>> size(a)
ans =
1 3
I was looking for something along what you wanted, but wanted to put it back into a variable.
So this is what I did
variable = ['hello this is x' x ', this is now y' y ', finally this is d:' d]
basically
variable = [str1 str2 str3 str4 str5 str6]