I have a very large data frame where some values are associated to a factor, like this:

```
value user
12 USER1
4 USER5
6 USER3
50 USER1
2 USER2
1 USER1
8 USER5
9 USER3
55 USER1
15 USER2
```

I want to find out the max and min of the value for each user. I tried with a for loop, where I create a temp variable and find max and min there, going through the user list. However, the size of the database is quite big (100Mb) and it takes a really long time (30 mins). Is there a smarter way to do this? Thanks.

Answer:

If df is your original `data.frame`

for "big" data it is recommended to use `data.table`

package:

```
library(data.table)
dt = data.table(df)
setkey(dt, user)
dt[,list(min(value), max(value)),by=user]
user V1 V2
1: USER1 1 55
2: USER5 4 8
3: USER3 6 9
4: USER2 2 15
```

**Edit**: good example to use `each`

from `plyr`

!

```
> library(plyr)
> dt[,as.list(each(min,max)(value)),by=user]
user min max
1: USER1 1 55
2: USER5 4 8
3: USER3 6 9
4: USER2 2 15
```

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