Update Counter collection in python with string, not letter

How to update a Counter with a string, not the letters of the string? For example, after initializing this counter with two strings:

from collections import Counter c = Counter(['black','blue']) 

"add" to it another string such as 'red'. When I use the update() method it adds the letters 'r','e','d':

c.update('red') c >>Counter({'black': 1, 'blue': 1, 'd': 1, 'e': 1, 'r': 1}) 

6 Answers

You can update it with a dictionary, since add another string is same as update the key with count +1:

from collections import Counter c = Counter(['black','blue']) c.update({"red": 1}) c # Counter({'black': 1, 'blue': 1, 'red': 1}) 

If the key already exists, the count will increase by one:

c.update({"red": 1}) c # Counter({'black': 1, 'blue': 1, 'red': 2}) 

c.update(['red']) >>> c Counter({'black': 1, 'blue': 1, 'red': 1}) 

Source can be an iterable, a dictionary, or another Counter instance.

Although a string is an iterable, the result is not what you expected. First convert it to a list, tuple, etc.

You can use:

c["red"]+=1 # or c.update({"red": 1}) # or c.update(["red"]) 

All these options will work regardless of the key being present or not. And if present, they will increase the count by 1

I though it would be also good to give another example which you can both increase and decrease the number of counts

from collections import Counter counter = Counter(["red", "yellow", "orange", "red", "orange"]) # to increase the count counter.update({"yellow": 1}) # or counter["yellow"] += 1 # to decrease counter.update({"yellow": -1}) # or counter["yellow"] -= 1 

Try this:

c.update({'foo': 1}) 

I just ran into the same problem recently. You can also put it in a tuple like this.

c.update(('red',)) 

The previous answers haven't suggested this alternative, so I might as well post it here.