I have a folder with 1000 tifs. I'd like to read 4 tifs, do some calculation and read the next 4 tifs. The problem is, that for example tif number 500 is missing. Now my current program stops right bevor tif number 500.
So my idea is that I check if the path exists with file_test and /directory and skip all missing values in the foor loop.
Directory: Set this keyword to return 1 (true) if File exists and is a directory. true =1, false = 0
for j = 0, 1102 do begin
PathEx = File_test(e:\Meteosat\Tiff\2016\06\17\MSG_201606170100_B4_L.tif', directory)
if PathEx = 1 then
B = READ_TIFF(e:\Meteosat\Tiff\2016\06\17\MSG_201606170100_B4_L.tif, GEOTIFF=tags)
if PathEx = 0 then
print, 'missing' and continue
end
I want to skip all missing paths. I don't know how to do this. I Also read something about
.CONTINUE
But I have no clue how this works too.
thank you!
pampi
I am not sure you are using the correct syntax. Your code should be something like the following:
FOR j=0L, 1102L DO BEGIN
PathEx = FILE_TEST('e:\Meteosat\Tiff\2016\06\17\MSG_201606170100_B4_L.tif', /DIRECTORY)
IF (PathEx[0] EQ 0) THEN CONTINUE ;; This will jump to the next index
b = READ_TIFF('e:\Meteosat\Tiff\2016\06\17\MSG_201606170100_B4_L.tif',GEOTIFF=tags)
ENDFOR
You should probably have a list of file names and then index those. Suppose you call them something like filenames and this is a [N]-element string array. Then you would do something like the following within the above loop:
file = filenames[j]
PathEx = FILE_TEST(file[0],/DIRECTORY)
IF (PathEx[0] EQ 0) THEN CONTINUE ;; This will jump to the next index
b = READ_TIFF(file[0],GEOTIFF=tags)
I should also mention that the variable b should either be an array or you should have an array defined outside the loop that you can store data into, otherwise all your operations within the FOR loop will be lost.
Related
New to Julia, trying to simply ask the user to choose 5 numbers and put it into an array and print the array. My output only says pick 5 numbers with "nothing" followed underneath. I cant seem to figure out why it wont read my inputs.
function ask()
lst = []
i = 0
println("pick 5 numbers to add to a list")
while i < 5
choice = readline
choice = push!(lst, choice);
i += 1
end
end
println(ask())
You were assigning function reference to list elements rather than calling the function.
This should be:
function ask()
lst = String[]
i = 0
println("pick 5 numbers to add to a list")
while i < 5
choice = readline()
choice = push!(lst, choice);
i += 1
end
lst
end
If you want numbers rather than Strings the last line could be parse.(Int, lst) or you could add this conversion near readline
Note that if you do not plan to introduce some error checking etc. this all code could be simply written as:
println("pick 5 numbers to add to a list")
lst = [parse(Int, readline()) for _ in 1:5]
I am new to Elixir language and I am having some issues while writing a piece of code.
What I am given is a 2D array like
list1 = [
[1 ,2,3,4,"nil"],
[6,7,8,9,10,],
[11,"nil",13,"nil",15],
[16,17,"nil",19,20] ]
Now, what I've to do is to get all the elements that have values between 10 and 20, so what I'm doing is:
final_list = []
Enum.each(list1, fn row ->
Enum.each(row, &(if (&1 >= 10 and &1 <= 99) do final_list = final_list ++ &1 end))
end
)
Doing this, I'm expecting that I'll get my list of numbers in final_list but I'm getting blank final list with a warning like:
warning: variable "final_list" is unused (there is a variable with the same name in the context, use the pin operator (^) to match on it or prefix this variable with underscore if it is not meant to be used)
iex:5
:ok
and upon printing final_list, it is not updated.
When I try to check whether my code is working properly or not, using IO.puts as:
iex(5)> Enum.each(list1, fn row -> ...(5)> Enum.each(row, &(if (&1 >= 10 and &1 <= 99) do IO.puts(final_list ++ &1) end))
...(5)> end
...(5)> )
The Output is:
10
11
13
15
16
17
19
20
:ok
What could I possibly be doing wrong here? Shouldn't it add the elements to the final_list?
If this is wrong ( probably it is), what should be the possible solution to this?
Any kind of help will be appreciated.
As mentioned in Adam's comments, this is a FAQ and the important thing is the message "warning: variable "final_list" is unused (there is a variable with the same name in the context, use the pin operator (^) to match on it or prefix this variable with underscore if it is not meant to be used)" This message actually indicates a very serious problem.
It tells you that the assignment "final_list = final_list ++ &1" is useless since it just creates a local variable, hiding the external one. Elixir variables are not mutable so you need to reorganize seriously your code.
The simplest way is
final_list =
for sublist <- list1,
n <- sublist,
is_number(n),
n in 10..20,
do: n
Note that every time you write final_list = ..., you actually declare a new variable with the same name, so the final_list you declared inside your anonymous function is not the final_list outside the anonymous function.
for my code I want all numbers from a dictionary under 70 to be deleted, I'm unsure of how to specify this and I need it to also delete the associated name with that number as well, either that or only diplay numbers that are 70 or above.
Below is the code that I have in it's entirety:
name = []
number =[]
name_grade = {}
counter = 0
counter_bool= True
num_loop = True
while counter_bool:
stu = int(input("please enter the number of students: "))
if stu < 2:
print("value is too low, try again")
continue
else:
break
while counter != stu:
name_inp = str(input("Enter your name: "))
while num_loop:
number_inp = int(input("Enter your number: "))
if number_inp < 0 or number_inp > 100:
print("The value is too high or too low, please enter a number between 0 and 100.")
continue
else:
break
name_grade[name_inp] = number_inp
name.append(name_inp)
number.append(number_inp)
counter += 1
print(name_grade)
sorted_numbers = sorted(name_grade.items(), key= lambda x:x[1])
print(sorted_numbers)
if number > 70:
resorted_numbers = number < 70
print(resorted numbers)
how would I go about this?
Also if it's also not too much trouble could someone explain in detail about dictionary keys and how the lambda function I've used works? I got help but I would prefer to know the small details on how it's applied and formatted but don't worry if it's a pain to explain.
You can just iterate over the dictionary and filter for values less than 70:
resorted_numbers = {k:v for k,v in name_grade.items() if v<70}
dict.items method returns a list of key-value tuple pairs of a dictionary, so the lambda function is telling the sorted function to sort by the second element in each tuple.
I would like to iterate over a list and occasionally delete items of said list. Below a toy example:
function delete_item!(myarray, item)
deleteat!(myarray, findin(myarray, [item]))
end
n = 1000
myarray = [i for i = 1:n];
for a in myarray
if a%2 == 0
delete_item!(myarray, a)
end
end
However I get error:
BoundsError: attempt to access 500-element Array{Int64,1} at index [502]
How can I fix it (as efficiently as possible)?
Additional information. The above seems like a silly example, in my original problem I have a list of agents which interact. Therefore I am not sure if iterating over a copy would be the best solution. For example:
#creating my agent
mutable struct agent <: Any
id::Int
end
function delete_item!(myarray::Array{agent, 1}, item::agent)
deleteat!(myarray, findin(myarray, [item]))
end
#having my list of agents
n = 1000
myarray = agent[agent(i) for i = 1:n];
#trying to remove agents from list while having them interact
for a in myarray
#agent does stuff
if a.id%2 == 0 #if something happens remove
delete_item!(myarray, a)
end
end
Unfortunately there is no single answer to this question as most efficient approach depends on the logic of the whole model (in particular do other agents' actions depend on the fact that some entry is actually deleted from an array).
In most cases the following approach should be the simplest (I am leaving findin which is inefficient but I understand that you may have duplicates in myarray in general):
n = 1000
myarray = [i for i = 1:n];
keep = trues(n)
for (i, a) in enumerate(myarray)
keep[i] || continue # do not process an agent that is marked for deletion
if a%2 == 0 # here application logic might also need to check keep in some cases
keep[findin(myarray, [a])] = false
end
end
myarray = myarray[keep]
If for some reason you really need to delete elements of myarray in each iteration here is how you can do it:
n = 1000
myarray = [i for i = 1:n];
i = 1
while i <= length(myarray)
a = myarray[i]
if a%2 == 0
todelete = findin(myarray, [a])
i -= count(x -> x < i, todelete) # if myarray has duplicates of a you have to move the counter back
deleteat!(myarray, todelete)
else
i += 1
end
end
In general the code you give will not be very fast (e.g. if you know myarray does not contain duplicates it can be much simpler - and I guess you can).
EDIT: Here is how you can implement both versions if you know you do not have duplicates (you can simply use agent's index - observe that we can also avoid unnecessary checks):
n = 1000
myarray = [i for i = 1:n];
keep = trues(n)
for (i, a) in enumerate(myarray)
if a%2 == 0 # here application logic might also need to check keep in some cases
keep[i] = false
end
end
myarray = myarray[keep]
If for some reason you really need to delete elements of myarray in each iteration here is how you can do it:
n = 1000
myarray = [i for i = 1:n];
i = 1
while i <= length(myarray)
a = myarray[i]
if a%2 == 0
deleteat!(myarray, i)
else
i += 1
end
end
So I have a table that holds references to other tables like:
local a = newObject()
a.collection = {}
for i = 1, 100 do
local b = newObject()
a[#a + 1] = b
end
Now if I want to see if a particular object is within "a" I have to use pairs like so:
local z = a.collection[ 99 ]
for i,j in pairs( a.collection ) do
if j == z then
return true
end
end
The z object is in the 99th spot and I would have to wait for pairs to iterate all the way throughout the other 98 objects. This set up is making my program crawl. Is there a way to make some sort of key that isn't a string or a table to table comparison that is a one liner? Like:
if a.collection[{z}] then return true end
Thanks in advance!
Why are you storing the object in the value slot and not the key slot of the table?
local a = newObject()
a.collection = {}
for i = 1, 100 do
local b = newObject()
a.collection[b] = i
end
to see if a particular object is within "a"
return a.collection[b]
If you need integer indexed access to the collection, store it both ways:
local a = newObject()
a.collection = {}
for i = 1, 100 do
local b = newObject()
a.collection[i] = b
a.collection[b] = i
end
Finding:
local z = a.collection[99]
if a.collection[z] then return true end
Don't know if it's faster or not, but maybe this helps:
Filling:
local a = {}
a.collection = {}
for i = 1, 100 do
local b = {}
a.collection[b] = true -- Table / Object as index
end
Finding:
local z = a.collection[99]
if a.collection[z] then return true end
If that's not what you wanted to do you can break your whole array into smaller buckets and use a hash to keep track which object belongs to which bucket.
you might want to consider switching from using pairs() to using a regular for loop and indexing the table, pairs() seems to be slower on larger collections of tables.
for i=1, #a.collection do
if a.collection[i] == z then
return true
end
end
i compared the speed of iterating through a collection of 1 million tables using both pairs() and table indexing, and the indexing was a little bit faster every time. try it yourself using os.clock() to profile your code.
i can't really think of a faster way of your solution other than using some kind of hashing function to set unique indexes into the a.collection table. however, doing this would make getting a specific table out a non-trivial task (you wouldn't just be able to do a.collection[99], you'd have to iterate through until you found one you wanted. but then you could easily test if the table was in a.collection by doing something like a.collection[hashFunc(z)] ~= nil...)