# Convert foreign currency valuations

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One of the most common problems when dealign with financial data is to have assets (or liabilities) denominated in a currency that is different from the domestic one.

I propose a tidy solution to this problem that involves no use of for cycles.

The principle of the solution is that converting each currency can be done in parallel using the **map** function while the consolidation of the results will be done using the **reduce** logic.

I am a big fan of the tidyverse and therefore I will start loading the required packages

library(purrr) library(stringr) library(tibble) library(magrittr) library(dplyr)

I suppose to have a very simple investment dataset made of two fields:

- a column with the currency of the investment (local currency being
*EUR*) - a column with the market value of the investment in local currency

Investments <- tibble(ccy = c(rep("EUR",2), rep("JPY",3), rep("GBP",3)), local_MV = c(1.5e6,1.2e6,2e8,1.5e8,3e8,1e6,1.5e6,2e6)) %>% mutate(local_MV = as.double(local_MV)) %>% mutate(EUR_MV = local_MV) Investments ## # A tibble: 8 x 3 ## ccy local_MV EUR_MV #### 1 EUR 1500000 1500000 ## 2 EUR 1200000 1200000 ## 3 JPY 200000000 200000000 ## 4 JPY 150000000 150000000 ## 5 JPY 300000000 300000000 ## 6 GBP 1000000 1000000 ## 7 GBP 1500000 1500000 ## 8 GBP 2000000 2000000

I then store in a list the current currency FX rates

FX <- list("JPY" = 130, "GBP" = 0.8)

The first part of the algorithm consists in finding the rows of the Investments database which are subject to FX conversion for each of the currencies that are stored in the **FX** list using the *stringr* function *str_which*.

This is the “parallel” part of the algorithm because it can be done currency by currency independently. We therefore use the *map* function of the *purrr* package.

pos_ccy <- map(names(FX), ~str_which(Investments$ccy,.)) %>% set_names(names(FX)) pos_ccy ## $JPY ## [1] 3 4 5 ## ## $GBP ## [1] 6 7 8

This list contains the row numbers for which there is an investment denominated in each of the currencies in the FX universe.
We then use this information together with the actual FX rate to convert the investments’ local market value. We now use the *map2* function.

converted_MV <- map2(pos_ccy, FX ,~Investments$local_MV[.x]/.y) converted_MV ## $JPY ## [1] 1538462 1153846 2307692 ## ## $GBP ## [1] 1250000 1875000 2500000

We can notice that we now have a list made by two different vectors of converted market values. We need to consolidate those into the EUR_MV column in the Investments dataset.

This is the second step of the algorithm that uses the *reduce* function of *purrr*

Investments$EUR_MV[pos_ccy %>% reduce(c)] <- converted_MV %>% reduce(c) Investments ## # A tibble: 8 x 3 ## ccy local_MV EUR_MV #### 1 EUR 1500000 1500000 ## 2 EUR 1200000 1200000 ## 3 JPY 200000000 1538462. ## 4 JPY 150000000 1153846. ## 5 JPY 300000000 2307692. ## 6 GBP 1000000 1250000 ## 7 GBP 1500000 1875000 ## 8 GBP 2000000 2500000

This function modifies rows of the EUR_MV field by reducing the lists from the map functions into vectors.

We can notice that the EUR positions have not changed their market value.

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