with-statement

I have the following dataset (simple version of my actual data), 'data', and would like to calculate weighted means for variables x1 and x2, using weightings w1 and w2 respectively, split up into two groups (groups determined by the variable n). data <- data.frame(n = c(1,1,1,2,2,2), x1 = c(4,5,4,7,5,5), x2 = c(7,10,9,NaN,11,12), w1 = c(0,1,1,1,1,1), w2 = c(1,1,1,0,0,1)) I'm trying to do it using with() but get an error when I run this: with(data, aggregate(x = list(x1=x1, x2=x2), by = list(n = n), FUN = weighted.mean, w = list(w1 = w1,w2 = w2))) On the otherhand, if weights aren't specified

Does anyone have a real world example outside of python's file object implementation of an __enter__ and __exit__ use case? Preferably your own, since what I'm trying to achieve is a better way to conceptualize the cases where it would be used. I've already read this . And, here's a link to the python documentation. There are many uses. Just in the standard library we have: sqlite3 ; using the connection as a context manager translates to committing or aborting the transaction. unittest ; using assertRaises as a context manager lets you assert an exception is raised, then test aspects of the

Is this code with open(myfile) as f: data = f.read() process(data) equivalent to this one try: f = open(myfile) data = f.read() process(f) finally: f.close() or the following one? f = open(myfile) try: data = f.read() process(f) finally: f.close() This article: http://effbot.org/zone/python-with-statement.htm suggests (if I understand it correctly) that the latter is true. However, the former would make more sense to me. If I am wrong, what am I missing? It's equivalent to the latter one, because until open() successfully returns, f has no value, and should not be closed. According to the

I am wondering if there is something similar to javascript or VB's with statement but in php The way this works, for example in VB is shown below. The two code snippets do the same effect: array[index].attr1 = val1; array[index].attr2 = val2; array[index].attr3 = val3; is equal to : With(array[index]) .attr1 = val1 .attr2 = val2 .attr3 = val3 End With Not exactly the with statement, but you can use references in your example: $r = &$array[index]; $r->attr1 = val1; $r->attr2 = val2; $r->attr3 = val3; If needed with arrays as in your example, you can mimic the with statement by using the array

I am trying to understand the trade offs/differences between these to ways of opening files for line-by-line processing with open('data.txt') as inf: for line in inf: #etc vs for line in open('data.txt'): # etc I understand that using with ensures the file is closed when the "with-block" (suite?) is exited (or an exception is countered). So I have been using with ever since I learned about it here. Re for -loop: From searching around the net and SO, it seems that whether the file is closed when the for -loop is exited is implementation dependent? And I couldn't find anything about how this