r - How to assign output of cat to an object?

Question

How would it be possible in the example below to skip the step of writing to file "test.txt", i.e. assign the cat-result to an object, and still achieve the same end result?

I thought I'd include the full example to give background to my problem.

test <- c("V 1", "x", "1 2 3", "y", "3 5 8", "V 2", "x", "y", "V 3", "y", "7 2 1", "V 4", "x", "9 3 7", "y")

# Write selection to file
cat(test, "
", file="test.txt")
test2 <- readLines("test.txt")
test3 <- strsplit(test2, "V ")[[1]][-1]

# Find results
x <- gsub("([0-9]) (?:x )?([0-9] [0-9] [0-9])?.*", "\1 \2 ", test3, perl = TRUE)
y <- gsub("([0-9]).* y ?([0-9] [0-9] [0-9])?.*", "\1 \2 ", test3, perl = TRUE)

# Eliminate tests with no results
x1 <- x[regexpr("[0-9] ([^0-9]).*", x) == -1]
y1 <- y[regexpr("[0-9] ([^0-9]).*", y) == -1]

# Dataframe of results
xdf1 <- read.table(textConnection(x1), col.names=c("id","x1","x2","x3"))
ydf1 <- read.table(textConnection(y1), col.names=c("id","y1","y2","y3"))
closeAllConnections()

# Dataframe of tests with no results
x2 <- x[regexpr("[0-9] ([^0-9]).*", x) == 1]
y2 <- y[regexpr("[0-9] ([^0-9]).*", y) == 1]

df1 <- as.integer(x2[x2 == y2])
df1 <- data.frame(id = df1)

# Merge dataframes
results <- merge(xdf1, ydf1, all = TRUE)
results <- merge(results, df1, all = TRUE)
results

Results in:

  id x1 x2 x3 y1 y2 y3
1  1  1  2  3  3  5  8
2  2 NA NA NA NA NA NA
3  3 NA NA NA  7  2  1
4  4  9  3  7 NA NA NA

Answer 1

As a more general solution, you can use the capture output function. It results in a character vector with elements corresponding to each line of the output.

your example:

test2<-capture.output(cat(test))

here is a multi-line example:

> out<-capture.output(summary(lm(hwy~cyl*drv,data=mpg)))
> out
 [1] ""                                                               
 [2] "Call:"                                                          
 [3] "lm(formula = hwy ~ cyl * drv, data = mpg)"                      
 [4] ""                                                               
 [5] "Residuals:"                                                     
 [6] "    Min      1Q  Median      3Q     Max "                       
 [7] "-8.3315 -1.4139 -0.1382  1.6479 13.5861 "                       
 [8] ""                                                               
 [9] "Coefficients:"                                                  
[10] "            Estimate Std. Error t value Pr(>|t|)    "           
[11] "(Intercept)  32.1776     1.2410  25.930  < 2e-16 ***"           
[12] "cyl          -2.0049     0.1859 -10.788  < 2e-16 ***"           
[13] "drvf          8.4009     1.8965   4.430 1.47e-05 ***"           
[14] "drvr          8.2509     6.4243   1.284    0.200    "           
[15] "cyl:drvf     -0.5362     0.3422  -1.567    0.119    "           
[16] "cyl:drvr     -0.5248     0.8379  -0.626    0.532    "           
[17] "---"                                                            
[18] "Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1 "
[19] ""                                                               
[20] "Residual standard error: 2.995 on 228 degrees of freedom"       
[21] "Multiple R-squared: 0.7524,Adjusted R-squared: 0.747 "         
[22] "F-statistic: 138.6 on 5 and 228 DF,  p-value: < 2.2e-16 "       
[23] ""