Calculating number and frequency of list elements in R?

Question

I've got a long list containing different numbers of elements which also can recur in the same field.
This is an example of the first five lines:

A <- list(c("JAMES","CHARLES","JAMES","RICHARD"),  
          c("JOHN","ROBERT","CHARLES"),  
          c("CHARLES","WILLIAM","CHARLES","MICHAEL","WILLIAM","DAVID","CHARLES","WILLIAM"),  
          c("CHARLES"),  
          c("CHARLES","CHARLES"))  

Now I'd like to calculate the number of elements for each line of the list.
My desired output would look similar to this:

[1] 4  
[2] 3  
[3] 7  
[4] 1  
[5] 2  

In addition to that I'd like to know the frequency the term "CHARLES" occurs in each line.
Based on my example I'd like to get an output similar to this:

[1] 1  
[2] 1  
[3] 3  
[4] 1  
[5] 2  

I thought of this:

> table(A)  
Error in table(A) : all arguments arguments must have same length  
> sum(A)  
Error in sum(A) : invalid 'type' (list) of argument  

But I don't know what to do about these error messages and am not aware of alternatives, unfortunately.
I know that the number of lines of the list is:

> length(A)  
[1] 5  

But this doesn't answer my question, unfortunately. I couldn't find any other answers, either.
Therefore I'd like to ask you to please help me calculate these two measures!

Thank you very much in advance!

Answer 1

You should get familiar with lapply and sapply to loop over lists:

sapply(A, length)
[1] 4 3 8 1 2

sapply(A, function(x)sum(grepl("CHARLES", x)))
[1] 1 1 3 1 2

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What grepl() does is to match a regular expression to your text, and returns TRUE or FALSE depending on whether there is a match. I then do a sum() over these logical values, i.e. summing the TRUE values.