sequences

问题 I have a multithreaded process which inserts several records into a single table. The inserts are performed in a stored procedure, with the sequence being generated INTO a variable, and that variable is later used inside of an INSERT . Given that I'm not doing mysequence.nextval inside the INSERT itself, it makes me think that it is possible for two concurrent processes to grab a sequence in one order, then do the inserts in the reverse order. If this is the case, then the sequence numbers

问题 How can i generate a sequence of numbers which are in Geometric Progression in R? for example i need to generate the sequence : 1, 2,4,8,16,32 and so on....till say a finite value? 回答1: Here's what I'd do: geomSeries <- function(base, max) { base^(0:floor(log(max, base))) } geomSeries(base=2, max=2000) # [1] 1 2 4 8 16 32 64 128 256 512 1024 geomSeries(3, 100) # [1] 1 3 9 27 81 回答2: Why not just enter 2^(0:n)? E.g. 2^(0:5) gets you from 1 to 32 and so on. Capture the vector by assigning to a

问题 So I'm writing a stored procedure and am having trouble getting the next value of a sequence into a variable. The sequence name is passed into the function and is stored as a varchar2 variable. How can you get the next value in that sequence into a local variable. 回答1: Something like this? create or replace procedure next_val (p_sequence_name varchar2) as v_nextval integer; v_select varchar2(100); begin v_select := 'select '||p_sequence_name||'.nextval from dual'; execute immediate v_select

问题 I have a table, foo . For the purposes of a quick upgrade/deploy of my site, I made a new table, tmp_foo , to contain some new data, by doing: create table tmp_foo (like foo including constraints including defaults including indexes); Now each table has a PK id column that looks like: Column | Type | Modifiers -------------+-----------------------+-------------------------------------------------------------------------- id | integer | not null default nextval('foo_id_seq'::regclass) The

问题 I have a postgres database that uses sequences extensively to generate primary keys of tables. After a lot of usage of this database i.e. Adding/Update/Delete operation the columns that uses sequences for primary keys now have a lot holes/gaps in them and the sequence value itself is very high. My question is: Are there any ways in which we can fix these gaps in Primary Keys? which should inturn bring down the max value of the number in that columns and then reset the sequence? Note: A lot of

问题 I am currently working with Keras using Tensorflow as the backend. I have a LSTM Sequence Prediction model shown below that I am using to predict one step ahead in a data series (input 30 steps [each with 4 features], output predicted step 31). model = Sequential() model.add(LSTM( input_dim=4, output_dim=75, return_sequences=True)) model.add(Dropout(0.2)) model.add(LSTM( 150, return_sequences=False)) model.add(Dropout(0.2)) model.add(Dense( output_dim=4)) model.add(Activation("linear")) model

问题 My question is simple: Is there an O(n) algorithm for finding the longest contiguous subsequence between two sequences A and B? I searched it, but all the results were about the LCS problem, which is not what I'm seeking. Note: if you are willing to give any sample code, you are more than welcome to do so, but please, if you can, in C or C++. Edit: Here is an example: A: { a, b, a, b, b, b, a } B: { a, d, b, b, b, c, n } longest common contiguous subsequence: { b, b, b } 回答1: Yes, you can do

问题 Assume you have a vector like so: v <- c(1,1,1,2,2,2,2,1,1,3,3,3,3) How can it be best reduced to a data.frame like this? v.df <- data.frame(value=c(1,2,1,3),repetitions=c(3,4,2,4)) In a procedural language I might just iterate through a loop and build the data.frame as I go, but with a large dataset in R such an approach is inefficient. Any advice? 回答1: or more simply data.frame(rle(v)[]) 回答2: with(rle(v), data.frame(values, lengths)) should get you what you need. values lengths 1 3 2 4 1 2

问题 Why there is no List.skip and List.take? There is of course Seq.take and Seq.skip, but they does not create lists as a result. One possible solution is: mylist |> Seq.skip N |> Seq.toList But this creates first enumerator then a new list from that enumerator. I think there could be more direct way to create a immutable list from immutable list. Since there is no copying of elements internally there are just references from the new list to the original one. Other possible solution (without

问题 What is an idiomatic way to merge (or retrieve the union of) two lists (or sequences) in Clojure? (merge l1 l2) doesn't seem to be the solution: a=> (merge '(1 2 3) '(2 3 4)) ((2 3 4) 1 2 3) 回答1: I think andih's solution works great. Here is an alternate way because hey why not. It uses concat and distinct: user> (distinct (concat '(1 2 3) '(2 3 4))) => (1 2 3 4) 回答2: One way to get the union of two lists is to use union Clojure> (into #{} (clojure.set/union '(1,2,3) '(3,4,5))) #{1 2 3 4 5}