apply a function to a data.frame column with condition

Thu, Mar 6, 2025 11:55 PM

On Thu, 06 Mar 2025, Arnaud Gaboury writes:

	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
??? )

I am sorry but I can't see where I shall put my df ? And my function to
get BTC price:
get_btc_price <- function(my_time) {
    # my_time_ms <- as.integer(as.numeric(my_time) * 1000)
    klines <- binance_klines("BTCUSDT", interval = '1h', start_time =
as.Date(my_time), end_time = as.Date(my_time) + 1)
    return(as.numeric(klines$close[[18]]))
}

Thank you for your help

Is the ticker you want to fetch data for always the
same?  If yes, then something like this could be
used. [I don't know/use binance, so with a 'dummy' of
your function.]

    get_btc_price <- function(my_time) {
        paste(42, my_time)
    }
    
    new.column <- mapply(
        function(symbol, mytime) {
            if (grepl("BTC$", symbol)) {
                get_btc_price(mytime)
            } else
                NA
        },
        portfolio$symbol,
        portfolio$time
    )

    ##                 BTCUSDT                  BTCUSDT 
    ##                      NA                       NA 
    ##                 ETHUBTC                  AAVEBTC 
    ##"42 2025-01-02 10:34:49" "42 2025-01-02 11:14:43" 
    ##                 ENAUSDT 
    ##                      NA

Enrico Schumann
Lucerne, Switzerland
https://enricoschumann.net

apply a function to a data.frame column with condition

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