R_ counting number of occurrence

Question

This is my data frame 'mydf'

n Results 1 l-m 2 m-m 3 l-m 4 l-m 5 l-m 6 l-m 7 l-m 8 l-m 9 l-m 10 l-m 11 m-l 12 l-m ...

there are thousands of rows. Now i want to count the number of occurrence of character strings 'l-m', 'm-m', 'm-l','l-l'(say this has 0 occurrence). I use the following method

table(mydf[,2]) h-h h-m l-m m-h m-m 11 7 29 2 13

But I want to get something like:

a=number of occurrence of 'l-m' b=number of occurrence of 'l-l' (even if it's zero) ...

I think a look at factor and levels may be relevant here. E.g. reply <- factor(c("yes", "yes"), levels = c("yes", "no")); table(reply). — Henrik
– Henrik, Commented Mar 31, 2014 at 11:56

Roland · Accepted Answer · 2014-03-31 12:27:25Z

Set the levels of your factor explicitely:

x <- factor(c("l-m","m-m","l-m","l-m","l-m","l-m","l-m","l-m","l-m","l-m","m-l","l-m"), levels=c("l-l", "m-m", "l-m", "m-l")) myTable <- table(x) #x #l-l m-m l-m m-l #0 1 10 1

You can then extract counts using standard subsetting:

myTable["m-m"] #m-m # 1

Thank you @Roland. From the result how can I abstract a single value. For example if I want to get the occurrence of 'm-m' and want to assign it for a variable 'a' how can I do it?

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