Locate the position of number


How to locate the first negative number?

For a list ["foo", "bar", "baz"] and an item in the list "bar" , what's the cleanest way to get its index 1 in Python? And the downside of this is that you will probably have a check for if the returned value is or is not None:. If you could have more occurrences, you'll not get complete information with list. If you have no occurrences, you can check for that with boolean check of the result, or just do nothing if you loop over the results:.

Pass that series of booleans to the series via subscript notation, and you get just the matching members:. Yes, you could use a list comprehension with enumerate too, but that's just not as elegant, in my opinion - you're doing tests for equality in Python, instead of letting builtin code written in C handle it:. If the value isn't there, catching the ValueError is rather verbose - and I prefer to avoid that. I'm usually iterating over the list anyways, so I'll usually keep a pointer to any interesting information, getting the index with enumerate. If you're munging data, you should probably be using pandas - which has far more elegant tools than the pure Python workarounds I've shown.

I do not recall needing list. However, I have looked through the Python standard library, and I see some excellent uses for it. The keyword module uses it to find comment markers in the module to automatically regenerate the list of keywords in it via metaprogramming. What these usages seem to have in common is that they seem to operate on lists of constrained sizes important because of O n lookup time for list.

While there are use-cases for it, they are fairly uncommon.

If you find yourself looking for this answer, ask yourself if what you're doing is the most direct usage of the tools provided by the language for your use-case. All indexes with the zip function:. With enumerate alist you can store the first element n that is the index of the list when the element x is equal to what you look for. This function takes the item and the list as arguments and return the position of the item in the list, like we saw before.

The nice thing about this approach is the function always returns a list of indices -- even if it is an empty list. It works with strings as well. After another year of heads-down python development, I'm a bit embarrassed by my original answer, so to set the record straight, one can certainly use the above code; however, the much more idiomatic way to get the same behavior would be to use list comprehension, along with the enumerate function.

And now, after reviewing this question and all the answers, I realize that this is exactly what FMc suggested in his earlier answer. At the time I originally answered this question, I didn't even see that answer, because I didn't understand it. I hope that my somewhat more verbose example will aid understanding. If the single line of code above still doesn't make sense to you, I highly recommend you Google 'python list comprehension' and take a few minutes to familiarize yourself.

It's just one of the many powerful features that make it a joy to use Python to develop code. A variant on the answer from FMc and user will give a dict that can return all indices for any entry:.

What is an Element?

You could also use this as a one liner to get all indices for a single entry. There are no guarantees for efficiency, though I did use set a to reduce the number of times the lambda is called. This solution is not as powerful as others, but if you're a beginner and only know about for loops it's still possible to find the first index of an item while avoiding the ValueError:. Note: Here we are iterating using i to get the indexes, but if we need rather to focus on the items we can switch to j.

So instead you can make it similar to the indexOf function of JavaScript which returns -1 if the item was not found:. One can convert the list lst to a numpy array. And, then use numpy. Following is the way in which you will implement it.

For those coming from another language like me, maybe with a simple loop it's easier to understand and use it:. I am thankful for So what exactly does enumerate do?


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That helped me to understand. It is mentioned in numerous answers that the built-in method of list. It is fine if you need to perform this once.

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But if you need to access the indices of elements a number of times, it makes more sense to first create a dictionary O n of item-index pairs, and then access the index at O 1 every time you need it. Thank you for your interest in this question. Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site the association bonus does not count.

Would you like to answer one of these unanswered questions instead? Learn more about Teams. In other words, we knew we wanted to "grab" two characters out of the middle of our sample string, and we knew those two characters always started in the fourth position of the string. Knowing that the middle string always starts in a certain position makes it easy to use the Mid function. But what do you do when the substring you want to extract could start anywhere within the string? As long as there's something in the string that identifies the start of the substring, you can use the Find function with the Mid function to accomplish the mission.

Use Find to generate the start point for the Mid function callHere's a simple example to demonstrate how this works.

Excel formula: Position of max value in list | Exceljet

Suppose you have a series of variable-length strings like those shown in Figure A. The only thing that's consistent in those strings is the presence of the dash or hyphen. Your challenge: You want to compose a formula that returns the first two characters following the dash. Figure A: You can use the Mid and Find functions to extract the first two characters following the dash in each of these entries. Here's the trick: You use the Find function to return the position of the dash in the string, and you use the Find function itself as the Mid function's first argument.


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We copied this Find function down the column so you can see that it returns a different value each time, depending on where the dash appears in the strings in column A. In order to extract the first two characters that follow the dash, you'll use the Find function to locate the dash and add 1 to that result. The Find function returns the location of the dash; you want to start extracting characters beginning at the next character, the one following the dash.

That formula says, in English, "Look at A2; determine the position of the dash in A2; add 1 to that value; then return the next two characters. To summarize, INDEX gets a value at a specified location in a range of cells based on numeric position.

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When the range is one-dimensional, you only need to supply a row number. When the range is two-dimensional, you'll need to supply both the row and column number. At this point, you may be thinking "So what? How often do you actually know the position of something in a spreadsheet? For example, we can use MATCH to get the position of the word "peach" in this list of fruits like this:. MATCH doesn't care if the list is horizontal or vertical. Match type is important and controls whether matching is exact or approximate.

The table below summarizes the options:. However, if you need an approximate match to lookup values along a scale, you'll want to use either 1 or -1, and you'll need to sort the lookup array according to your needs, [A-Z] when match type is 1, [Z-A] when match type is Approximate matching is useful when you want to find the best match in a scale of values, but it can be a disaster when you need an exact match. I recommend always setting match type explicitly to avoid unwelcome surprises.

Let's say we want to write a formula that returns the sales number for February for any given salesperson. Working one step at a time, let's leave the column hardcoded as 2 and make the row number dynamic.

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