R: add different values to columns within a list of dataframes

Question

If I have a list like:

list <- list( "1" = data.frame(time=1:3, temp = sample(11:13)),
              "3" = data.frame(time=1:3, temp = sample(11:13)))

list

$`1`
  time temp
1    1   11
2    2   12
3    3   13

$`3`
  time temp
1    1   11
2    2   12
3    3   13

Now I want to add a correction-value to columns temp, +1 for dataframe 1 and -1 for dataframe 3, so the result would be:

$`1`
  time temp
1    1   12
2    2   13
3    3   14

$`3`
  time temp
1    1   10
2    2   11
3    3   12

Let´s additionally assume I have multiple of those lists, where sometimes dataframe 3 or 1 may be missing, or even a dataframe 2 maybe included, which would need its own correction-factor... I tried strange things for dataframe 1:

list <- lapply(list, function(x)   {x <- x$"1"$temp-1;x})

or

list <- lapply(list, function(x)   {x <- x[x$temp+1,];x})

also tried to add a seq_along for the other dataframe in the list...nothing works, maybe because I don´t quite understand how the syntax works...

I'd give them a solid chance to edit what clearly is a snafu before downvoting...patience! — joran
– joran, Commented Aug 19, 2011 at 16:15
Ok I waited for the full question. But this is still too ambiguous to be answerable. Build a reproducible example that actually represents your full problem. — joran
– joran, Commented Aug 19, 2011 at 17:17
If this data is all the same size, it may be better to store it as a data.frame(), it would certainly simplify operations. If you want a quick and dirty way to convert back to a data.frame you can use df <- ldply(mylist) from the plyr package. — Brandon Bertelsen
– Brandon Bertelsen, Commented Aug 19, 2011 at 18:21

IRTFM · Accepted Answer · 2011-08-23 13:47:33Z

2

I changed the name of the data structure to dflist. It's just wrong to call a list "list". You also need some data structure to pull in the associated correction factors, so let's posit one with the same names as "dflist":

dflist <- list( "1" = data.frame(time=1:3, temp = sample(11:13)),
              "3" = data.frame(time=1:3, temp = sample(11:13)))

corrlist <- list("1" = 1, "3"=-1) 

# Replaced lapply with for loop
for( nam in names(dflist)) {
        dflist[[nam]]['temp'] <- dflist[[nam]]['temp'] +corrlist[[nam]]
                            }
 dflist

edited Aug 23, 2011 at 13:47

answered Aug 19, 2011 at 17:18

IRTFM

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6 Comments

Thomas Langkamp Over a year ago

Perfect, thanks! Except a missing bracket at the end - and it deletes/overwrites the names/numbers of the dataframes. Instead of $1 and $3 the dataframes are marked with [[1]] and [[2]]. If I return(dflist[x]) the names stay, but also those [[1]] are doubled O_o

IRTFM Over a year ago

The bracket was there (added space to emphasize) but there was a missing paren and your point about what I returned is well taken. Should have just returned dflist.

IRTFM Over a year ago

But other problems remain. Needs improvement.

Thomas Langkamp Over a year ago

Thanks for the loop. Looks as it should work....Unfortunately I also can´t figure out where the error is...

IRTFM Over a year ago

I don't get an error with that code. Is your R installation corrupted?

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