R - How to convert Date fields from 3 datasets with for loop?

Question

I'm trying to convert date field of 3 datasets using for loop and got the error:

Error in as.Date.default(mydatasets[i]$Date, "%Y-%m-%d") : do not know how to convert 'mydatasets[i]$Date' to class “Date”

Here's the code:

papel_BBD <-read.csv("http://ichart.finance.yahoo.com/table.csv?s=BBD",sep=",", header=1)
papel_HSBC <-read.csv("http://ichart.finance.yahoo.com/table.csv?s=HSBC",sep=",", header=1)
papel_ITAU <-read.csv("http://ichart.finance.yahoo.com/table.csv?s=ITUB",sep=",", header=1)


mydatasets <- c(papel_BBD, papel_HSBC, papel_ITAU)

for (i in 1:length(mydatasets)) {
  mydatasets[i]$Date <- as.Date(mydatasets[i]$Date, "%Y-%m-%d")
}

Console:

for (i in 1:length(mydatasets)) {
  mydatasets[i]$Date <- as.Date(mydatasets[i]$Date, "%Y-%m-%d")
}

Error in as.Date.default(mydatasets[i]$Date, "%Y-%m-%d") : do not know how to convert 'mydatasets[i]$Date' to class “Date”

I think I'm missing something in this line inside the for loop:

mydatasets[i]$Date <- as.Date(mydatasets[i]$Date, "%Y-%m-%d")

Thanks

Add a minimal data set with your question. Follow [this](https://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) question. — narendra-choudhary, Nov 15 '15 at 16:07
I think you need the format `as.Date(mydatasets[i]$Date, '%m/%d/%Y')` — akrun, Nov 15 '15 at 16:08
For that I need to know `mydatasets$Date`. The `%m/%d/%Y` part of `as.Date` depends on format of `mydatasets$Date` column. — narendra-choudhary, Nov 15 '15 at 16:13
I tried your code, it is reading the 'Date' in the `%Y-%m-%d` format for me. We need to only change the `factor` to `Date` class. — akrun, Nov 15 '15 at 16:24

akrun · Answer 1 · 2015-11-15T16:24:03.023

We can use lapply with the correct format (based on the urls) for the 'Date' column.

lst <- lapply(mget(ls(pattern='^papel\\_.*')), transform, 
               Date=as.Date(Date))
lapply(lst, head, 2)
#$papel_BBD
#        Date Open High  Low Close   Volume Adj.Close
#1 2015-11-13 5.64 5.68 5.51  5.58 15207900      5.58
#2 2015-11-12 5.61 5.78 5.59  5.64 11032800      5.64

#$papel_HSBC
#        Date  Open  High   Low Close  Volume Adj.Close
#1 2015-11-13 39.07 39.18 38.85 38.92 1922600     38.92
#2 2015-11-12 39.75 39.86 39.53 39.57 2020700     39.57

#$papel_ITAU
#        Date Open High  Low Close   Volume Adj.Close
#1 2015-11-13 7.36 7.41 7.11  7.14 15996600      7.14
#2 2015-11-12 7.36 7.51 7.30  7.36 14638300      7.36

It is better to keep the datasets in the list itself. If we need to reflect the changes in the original dataset, we can use list2env (not recommended though)

list2env(lst, envir=.GlobalEnv)

str(papel_BBD)
#'data.frame':   3346 obs. of  7 variables:
# $ Date     : Date, format: "2015-11-13" "2015-11-12" ...
# $ Open     : num  5.64 5.61 5.81 5.5 5.67 5.69 5.69 5.82 5.51 5.48 ...
# $ High     : num  5.68 5.78 5.81 5.75 5.71 5.83 5.85 5.86 5.86 5.55 ...
# $ Low      : num  5.51 5.59 5.63 5.41 5.53 5.61 5.65 5.61 5.51 5.38 ...
# $ Close    : num  5.58 5.64 5.81 5.65 5.6 5.83 5.81 5.67 5.83 5.53 ...
# $ Volume   : int  15207900 11032800 19484900 13652300 17659600 11074400 12065900 16797400 24521100 17566100 ...
# $ Adj.Close: num  5.58 5.64 5.81 5.65 5.6 ...

score 0 · Accepted Answer · answered Nov 15 '15 at 16:39

Try this

for(i in length(mydatasets)){
    if(is.factor(mydatasets[[i]])){
        mydatasets[[i]] <- as.Date(mydatasets[[i]])
    }
}

str(mydatasets)

## $ Date     : Date[1:3346], format: "2015-11-13" "2015-11-12" "2015-11-11" "2015-11-10" ...
## $ Open     : num [1:3346] 5.64 5.61 5.81 5.5 5.67 5.69 5.69 5.82 5.51 5.48 ...
## $ High     : num [1:3346] 5.68 5.78 5.81 5.75 5.71 5.83 5.85 5.86 5.86 5.55 ...
## $ Low      : num [1:3346] 5.51 5.59 5.63 5.41 5.53 5.61 5.65 5.61 5.51 5.38 ...
## $ Close    : num [1:3346] 5.58 5.64 5.81 5.65 5.6 5.83 5.81 5.67 5.83 5.53 ...
## $ Volume   : int [1:3346] 15207900 11032800 19484900 13652300 17659600 11074400 12065900 16797400 24521100 17566100 ...
## $ Adj.Close: num [1:3346] 5.58 5.64 5.81 5.65 5.6 ...
## $ Date     : Date[1:4111], format: "2015-11-13" "2015-11-12" "2015-11-11" "2015-11-10" ...
## $ Open     : num [1:4111] 39.1 39.8 39.9 39.5 40.3 ...
## ...

R - How to convert Date fields from 3 datasets with for loop?

2 Answers2