So, if I have a list called myList I use len(myList) to find the number of elements in that list. Fine. But how do I find the number of lists in a list?
text = open("filetest.txt", "r")
myLines = text.readlines()
numLines=len(myLines)
print numLines
The above text file used has 3 lines of 4 elements separated by commas. The variable numLines prints out as '4' not '3'. So, len(myLines) is returning the number of elements in each list not the length of the list of lists.
When I print myLines[0] I get the first list, myLines[1] the second list, etc. But len(myLines) does not show me the number of lists, which should be the same as 'number of lines'.
I need to determine how many lines are being read from the file.
"The above text file used has 3 lines of 4 elements separated by commas. The variable numLines prints out as '4' not '3'. So, len(myLines) is returning the number of elements in each list not the length of the list of lists."
It sounds like you're reading in a .csv with 3 rows and 4 columns. If this is the case, you can find the number of rows and lines by using the .split() method:
text = open("filetest.txt", "r").read()
myRows = text.split("\n") #this method tells Python to split your filetest object each time it encounters a line break
print len(myRows) #will tell you how many rows you have
for row in myRows:
myColumns = row.split(",") #this method will consider each of your rows one at a time. For each of those rows, it will split that row each time it encounters a comma.
print len(myColumns) #will tell you, for each of your rows, how many columns that row contains
if the name of your list is listlen then just type len(listlen). This will return the size of your list in the python.
The method len() returns the number of elements in the list.
list1, list2 = [123, 'xyz', 'zara'], [456, 'abc']
print "First list length : ", len(list1)
print "Second list length : ", len(list2)
When we run above program, it produces the following result -
First list length : 3 Second list length : 2
This saves the data in a list of lists.
text = open("filetest.txt", "r")
data = [ ]
for line in text:
data.append( line.strip().split() )
print "number of lines ", len(data)
print "number of columns ", len(data[0])
print "element in first row column two ", data[0][1]
You can do it with reduce:
a = [[1, 2, 3], [4, 5, 6], [7, 8, 9], [], [1, 2]]
print(reduce(lambda count, l: count + len(l), a, 0))
# result is 11
Source: Stackoverflow.com