{"id":809,"date":"2018-05-19T12:02:45","date_gmt":"2018-05-19T10:02:45","guid":{"rendered":"https:\/\/blogs.fu-berlin.de\/reseda\/?page_id=809"},"modified":"2018-09-25T10:30:58","modified_gmt":"2018-09-25T08:30:58","slug":"e03","status":"publish","type":"page","link":"https:\/\/blogs.fu-berlin.de\/reseda\/e03\/","title":{"rendered":"R – Exercise III"},"content":{"rendered":"

1) Create a matrix named m1<\/span> with three rows and five columns and all the numeric (integer) values from 6 to 20!<\/p>\n

\r\nm1 <- matrix(6:20, nrow = 3, ncol = 5)\r\n\r\nm1\r\n##      [,1] [,2] [,3] [,4] [,5]\r\n## [1,]    6    9   12   15   18\r\n## [2,]    7   10   13   16   19\r\n## [3,]    8   11   14   17   20\r\n<\/pre>\n
2) Multiply all elements in m1<\/span> by 0.5! Overwrite the matrix m1<\/span> with the result!<\/p>\n
\r\nm1 <- m1 * 0.5\r\n<\/pre>\n
3) Create another matrix m2<\/span> with one row and five columns and all the numeric (integer) values from 1 to 5!<\/p>\n
\r\nm2 <- matrix(1:5, nrow = 1, ncol = 5)\r\n\r\nm2\r\n##      [,1] [,2] [,3] [,4] [,5]\r\n## [1,]    1    2    3    4    5\r\n<\/pre>\n
4) Calculate the sum of all elements in m2<\/span>!<\/p>\n
\r\nsum(m2)\r\n## [1] 15\r\n<\/pre>\n
5) Combine m1<\/span> and m2<\/span> with rbing()<\/span>. Save the result as m3<\/span> and check the dimension of the new matrix!<\/p>\n
\r\nm3 <- rbind(m1, m2)\r\n\r\nm3\r\n##      [,1] [,2] [,3] [,4] [,5]\r\n## [1,]  3.0  4.5  6.0  7.5  9.0\r\n## [2,]  3.5  5.0  6.5  8.0  9.5\r\n## [3,]  4.0  5.5  7.0  8.5 10.0\r\n## [4,]  1.0  2.0  3.0  4.0  5.0\r\n\r\ndim(m3)\r\n## [1] 4 5\r\n<\/pre>\n
6) Index the 5th column of m3<\/span>!<\/p>\n
\r\nm3[ , 5]\r\n## [1]  9.0  9.5 10.0  5.0\r\n<\/pre>\n
7) Index the 2nd and 4th lines of m3<\/span>!<\/p>\n
\r\nm3[ c(2, 4), ]\r\n##      [,1] [,2] [,3] [,4] [,5]\r\n## [1,]  3.5    5  6.5    8  9.5\r\n## [2,]  1.0    2  3.0    4  5.0\r\n<\/pre>\n
8) Calculate the sums for all columns in m3<\/span>!<\/p>\n
\r\ncolSums(m3)\r\n## [1] 11.5 17.0 22.5 28.0 33.5\r\n<\/pre>\n
9) Calculate the standard deviation for the 3rd column in m3<\/span>!<\/p>\n
\r\nsd( m3[ , 3] )\r\n## [1] 1.796988\r\n<\/pre>\n
10) From m3<\/span>, index the element in the 2nd column and 2nd line and all eight adjacent elements! Save the result as m4<\/span> and examine its object class!<\/p>\n
\r\nm4 <- m3[2:4, 2:4]\r\n\r\nm4\r\n##      [,1] [,2] [,3]\r\n## [1,]  5.0  6.5  8.0\r\n## [2,]  5.5  7.0  8.5\r\n## [3,]  2.0  3.0  4.0\r\n\r\nclass(m4)\r\n## [1] "matrix"\r\n<\/pre>\n
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