Selecting elements from Data Frame which meet an if condition inside a For Loop R

Question

I'm working with a data frame inside a function,and I have a problem in the syntaxis. This is the frame I'm working with:

And this is the code I'm using.

threshold=250
c
for (i in c[1]){ 
    if(threshold > any(c[i,2])){
        print(c[i,1])
    }
}

What I want is to get the first element of the data frame is the condition is met, but I get the result: [1] 1 2 3 4 5 6 7 8 9 10. It only has to be: 1 3 6 8 10

Any help would be appreciated. Thanks in advance.

`c` is a function. It may be better to name objects with other names — akrun, May 15 '15 at 13:41
possible duplicate of [Filtering a data frame in R](http://stackoverflow.com/questions/1686569/filtering-a-data-frame-in-r) — Frank, May 15 '15 at 14:04

score 1 · Answer 1 · answered May 15 '15 at 13:47

1

Use which

c[which(c$nobs<250),1]

answered May 15 '15 at 13:47

Shenglin Chen

4,504
11
11

1

why do you need `which`? – akrun May 15 '15 at 13:49
It is, but when you say `Use which`, it might imply that it is necessary – akrun May 15 '15 at 14:11

score 0 · Answer 2 · answered May 15 '15 at 13:41

0

subset(c, nobs > threshold)

answered May 15 '15 at 13:41

Quinn Weber

927
5
10

user227710 · Answer 3 · 2015-05-15T13:50:05.720

0

Not sure:

#df is your dataframe

option1:

 with(df,ifelse(nobs<250,lag(id,1),NA))
     [1]  1 NA  3 NA NA  6 NA  8 NA 10

option 2:

df[df$nobs<250,"id"]
[1]  1  3  6  8 10

edited May 15 '15 at 13:50

answered May 15 '15 at 13:42

user227710

3,164
18
35

score 0 · Accepted Answer · answered May 15 '15 at 13:45

0

Let's call your data.frame x to avoid the conflict of the function name c.

Following your syntax, it should be:

for (i in seq_len(nrow(x))){ 
    if(threshold > x[i,2]){
        print(x[i,1])
    }
}

Or simply,

x[x[,2] < threshold, 1]

answered May 15 '15 at 13:45

xb.

1,617
11
16

This one actually did exactly what I was looking for, thank you very much! Besides that, would you kindly explain me the difference between using" for (i in c[1]){" (mine) and using "for (i in seq_len(nrow(x))){" ? – hachondeoro May 15 '15 at 14:20
@Frank `i in x[1]` loops over the elements of the 1st column, while `i in seq_len(nrow(x))` loops over the index of the rows. If the 1st column is extactly the row indexes, as in your case, there is no difference. The major issue of the initial code is the use of `any`. `any` returns `TRUE` for any non-`FALSE`/`0`/`NULL (or other empty)` R object. Therefore `threshold > any(x[i,2])` is always `TRUE` in your example. – xb. May 15 '15 at 16:12

Selecting elements from Data Frame which meet an if condition inside a For Loop R

4 Answers4