Changing values on one dataframe based on data in another dataframe

Question

I have two data frames as follows:

test1 <- structure(list(`0.62m` = c(0.011, 0.043, 0.057, 0.067, 0.095, 
0.121, 0.098, 0.086, 0.103, 0.12, 0.104), `0.87m` = c(0.017, 
0.018, 0.052, 0.062, 0.111, 0.101, 0.112, 0.096, 0.104, 0.108, 
0.111), `1.12m` = c(0.009, 0.016, 0.048, 0.03, 0.085, 0.07, 0.108, 
0.076, 0.078, 0.092, 0.107), `1.37m` = c(0.025, 0.035, 0.035, 
0.048, 0.067, 0.074, 0.095, 0.08, 0.082, 0.091, 0.094)), .Names = c("0.62m", 
"0.87m", "1.12m", "1.37m"), row.names = 25:35, class = c("tbl_df", 
"tbl", "data.frame"))

#Test 2
test2 <- structure(list(`0.62m` = c(235.15, 230.95, 251.95, 261.25, 254.55, 
251.75, 259.85, 257.65, 252.55, 255.55, 254.15), `0.87m` = c(287.95, 
196.35, 275.05, 245.85, 253.35, 259.75, 254.95, 261.75, 253.05, 
264.45, 264.25), `1.12m` = c(36.35, 242.95, 266.65, 266.45, 248.85, 
256.95, 253.75, 268.25, 251.05, 268.85, 259.65), `1.37m` = c(20.65, 
287.95, 260.25, 260.55, 255.25, 258.45, 248.45, 261.95, 253.45, 
263.25, 252.05)), .Names = c("0.62m", "0.87m", "1.12m", "1.37m"
), row.names = 25:35, class = c("tbl_df", "tbl", "data.frame"
))

Test 1 looks like following:

   0.62m 0.87m 1.12m 1.37m
25 0.011 0.017 0.009 0.025
26 0.043 0.018 0.016 0.035
27 0.057 0.052 0.048 0.035
28 0.067 0.062 0.030 0.048
29 0.095 0.111 0.085 0.067
30 0.121 0.101 0.070 0.074
31 0.098 0.112 0.108 0.095
32 0.086 0.096 0.076 0.080
33 0.103 0.104 0.078 0.082
34 0.120 0.108 0.092 0.091
35 0.104 0.111 0.107 0.094

Test 2 looks like following:

    0.62m  0.87m  1.12m  1.37m
25 235.15 287.95  36.35  20.65
26 230.95 196.35 242.95 287.95
27 251.95 275.05 266.65 260.25
28 261.25 245.85 266.45 260.55
29 254.55 253.35 248.85 255.25
30 251.75 259.75 256.95 258.45
31 259.85 254.95 253.75 248.45
32 257.65 261.75 268.25 261.95
33 252.55 253.05 251.05 253.45
34 255.55 264.45 268.85 263.25
35 254.15 264.25 259.65 252.05

Now, I want to create a new dataframe test3 where I need to check if values in test2 is greater than 180 or not. If the value is greater than 180, then the elements should be same as test1 else it should be -1 * test1.

The desired ouput would look like following:

    0.62m 0.87m 1.12m 1.37m
25 0.011 0.017 -0.009 -0.025
26 0.043 0.018 0.016 0.035

I tried following:

test3 <- ifelse(test2 > 180, test1, -1 * test1)

Another method:

test3 <- data.frame(sapply(X = test1, FUN = function(x) (ifelse(test2>180, x, - 1*x))))

I think I need to use apply but not sure how to use that properly.

Answer 1

You just need some as.matrix() calls (note that only the two rightmost cells in the top row are actually less than 180):

ifelse(as.matrix(test2)>180,as.matrix(test1),-as.matrix(test1));
##    0.62m 0.87m  1.12m  1.37m
## 25 0.011 0.017 -0.009 -0.025
## 26 0.043 0.018  0.016  0.035
## 27 0.057 0.052  0.048  0.035
## 28 0.067 0.062  0.030  0.048
## 29 0.095 0.111  0.085  0.067
## 30 0.121 0.101  0.070  0.074
## 31 0.098 0.112  0.108  0.095
## 32 0.086 0.096  0.076  0.080
## 33 0.103 0.104  0.078  0.082
## 34 0.120 0.108  0.092  0.091
## 35 0.104 0.111  0.107  0.094

The return value will be a matrix, but you can get back to a data.frame (if you want) via as.data.frame().