2.10 Create labels - paste()

The paste() function is used to add characters together. It also works with numbers and dates which will automatically be converted to characters before being pasted together into a single label. See this example where we use all variables from typesdata to create a new column called plot_label (we select() for printing space):

typesdata %>% 
  mutate(plot_label = paste(id,
                            "was last measured at", date,
                            ", and the value was",    measurement)) %>% 
  select(plot_label)

## # A tibble: 3 x 1
##   plot_label                                                          
##   <chr>                                                               
## 1 ID1 was last measured at 2017-01-02 12:00:00 , and the value was 1.8
## 2 ID2 was last measured at 2018-02-03 13:00:00 , and the value was 4.5
## 3 ID3 was last measured at 2019-03-04 14:00:00 , and the value was 3.7

The paste is also useful when pieces of information are stored in different columns. For example, consider this made-up tibble:

pastedata <- tibble(year  = c(2007, 2008, 2009),
                   month = c("Jan", "Feb", "March"),
                   day   = c(1, 2, 3))

pastedata

## # A tibble: 3 x 3
##    year month   day
##   <dbl> <chr> <dbl>
## 1  2007 Jan       1
## 2  2008 Feb       2
## 3  2009 March     3

We can use paste() to combine these into a single column:

pastedata %>% 
  mutate(date = paste(day, month, year, sep = "-"))

## # A tibble: 3 x 4
##    year month   day date        
##   <dbl> <chr> <dbl> <chr>       
## 1  2007 Jan       1 1-Jan-2007  
## 2  2008 Feb       2 2-Feb-2008  
## 3  2009 March     3 3-March-2009

By default, paste() adds a space between each value, but we can use the sep = argument to specify a different separator. Sometimes it is useful to use paste0() which does not add anything between the values (no space, no dash, etc.).

We can now tell R that the date column should be parsed as such:

library(lubridate)

pastedata %>% 
  mutate(date = paste(day, month, year, sep = "-")) %>% 
  mutate(date = dmy(date))

## # A tibble: 3 x 4
##    year month   day date      
##   <dbl> <chr> <dbl> <date>    
## 1  2007 Jan       1 2007-01-01
## 2  2008 Feb       2 2008-02-02
## 3  2009 March     3 2009-03-03