apply a function to a data.frame column with condition

On Thu, 2025-03-06 at 07:29 +0100, Enrico Schumann wrote:

On Wed, 05 Mar 2025, Arnaud Gaboury writes:

I work with Binancer [1] and PMwR [2] packages to write a trading
journal.
Here is a sample of my data frame:
portfolio <- data.frame(
? symbol = c("BTCUSDT", "BTCUSDT", "ETHUBTC", "AAVEBTC",
"ENAUSDT"),
? time = c("2024-12-17 10:01:30", "2024-12-18 21:32:53", "2025-01-
02
10:34:49", "2025-01-02 11:14:43", "2025-01-02 11:15:22")
)

I want to fetch the 'BTCUSDT' price for a specific time if the
symbol
of same row end with these 3 letters : 'BTC'. In my sample, it will
be
rows 3 and 4.
Here is how I find BTCUSDT price for date 2025-01-02 10:34:49:

get_btc_price <- function(time) {
? klines <- binance_klines('BTCUSDT', start_time = '2025-01-02
10:34:49', end_time = '2025-01-02 10:34:49')
}

I was thinking of this code to write my new column BTCUSDT_price:

df <- portfolio %>%
? mutate(
??? BTCUSDT_price = ifelse(str_detect(symbol, "BTC$"),
map_dbl(time,
get_btc_price), NA_real_)
? )}

But the code returns:
Error in `mutate()`:
? In argument: `BTCUSDT_price = ifelse(...)`.
Caused by error in `map_dbl()`:
? In index: 1.
Caused by error in `[.data.table`:
! Item 1 of j is 12 which is outside the column number range
[1,ncol=0]

I have tried other workarounds but all give me errors.

Thank you for help


[1]https://cran.r-project.org/web/packages/binancer
[2]https://cran.r-project.org/web/packages/PMwR

You want to compute a new column for your data.frame as
a function of two existing columns.

In base R, if you don't want to use a loop (and there
would be nothing wrong with a loop), you could use
'mapply'; and then cbind the column to your data.frame:

??? new.column <- mapply(
??????? function(symbol, time) {
??????????? if (grepl("BTC$", symbol)) {
??????????????? ## your get_price computation, using
??????????????? ## 'symbol' and 'time'
??????????????? paste("do something with", symbol, time)
??????????????? 
??????????? } else
??????????????? NA
??????? },
??????? portfolio$symbol,
??????? portfolio$time
??? )

??? ## new.column
??? ##???????????????????????????????????????? BTCUSDT 
??? ##????????????????????????????????????????????? NA 
??? ##???????????????????????????????????????? BTCUSDT 
??? ##????????????????????????????????????????????? NA 
??? ##???????????????????????????????????????? ETHUBTC 
??? ## "do something with ETHUBTC 2025-01-02 10:34:49" 
??? ##???????????????????????????????????????? AAVEBTC 
??? ## "do something with AAVEBTC 2025-01-02 11:14:43" 
??? ##???????????????????????????????????????? ENAUSDT 
??? ##????????????????????????????????????????????? NA 

Thank you for your answer.
A very warm thanks for your PMwR package. It helps me managing my
portfolio in a professional way. Unfortunately there isn't so much
material to manage, follow, compute ratio etc. 
By any chance, do you have any cool build-in functions to cook monthly
data (PL, valuation etc) as we compute every month always the same data
?