Create function to count occurrences within groups in R

Question

I have a dataset with a unique ID for groups of patients called match_no and i want to count how many patients got sick in two different years by running a loop function to count the occurrences in a large dataset

for (i in db$match_no){(with(db, sum(db$TBHist16 == 1 & db$match_no == i))}

This is my attempt. I need i to cycle through each of the match numbers and count how many TB occurrences there was.

Can anyone correct my formula please.

Example here

df1 <- data.frame(Match_no = c(1, 1,1,1,1,2,2,2,2,2, 3,3,3,3,3, 4,4,4,4,4, 5,5,5,5,5),
                  var1 = c(1,1,1,0,0,1,1,1,0,0,0,1,1,1,1,1,0,0,0,1,1,1,1,0,1))

I want to count how many 1 values there are in each match number.

Thank you

Please provide a reproducible example with some data and an expected result — koolmees, Sep 09 '21 at 14:56
Does this answer your question? https://stackoverflow.com/q/1660124/12400385 — nniloc, Sep 09 '21 at 15:04

score 1 · Accepted Answer · answered Sep 09 '21 at 15:06

Some ideas:

Simple summary of all Match_no values:

xtabs(~var1 + Match_no, data = df1)
#     Match_no
# var1 1 2 3 4 5
#    0 2 2 1 3 1
#    1 3 3 4 2 4

Same as 1, but with a subset:

xtabs(~ Match_no, data = subset(df1, var1 == 1))
# Match_no
# 1 2 3 4 5 
# 3 3 4 2 4

Results in a frame:

aggregate(var1 ~ Match_no, data = subset(df1, var1 == 1), FUN = length)
#   Match_no var1
# 1        1    3
# 2        2    3
# 3        3    4
# 4        4    2
# 5        5    4

score 1 · Answer 2 · answered Sep 09 '21 at 15:10

1

In base R you can use aggregate and sum:

aggregate(var1 ~ Match_no, data = df1, FUN = sum)

  Match_no var1
1        1    3
2        2    3
3        3    4
4        4    2
5        5    4

answered Sep 09 '21 at 15:10

Clemsang

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Create function to count occurrences within groups in R

2 Answers2