Extract Matrix Column Values by Matrix Column Name

Extract matrix column values by matrix column name

Yes. But place your "test" after the comma if you want the column...

> A <- matrix(sample(1:12,12,T),ncol=4)

> rownames(A) <- letters[1:3]

> colnames(A) <- letters[11:14]
> A[,"l"]
 a  b  c 
 6 10  1 

see also help(Extract)

Extract column names for each value in column in matrix in R

We may use paste in a vectorized way by replicating the column names with col index and then get the unique after pasteing with the values of the n.mat (it is a data.frame after as.data.frame - so we used unlist)

unique(paste(colnames(n.mat)[col(n.mat)], unlist(n.mat), sep="_"))

-output

[1] "V1_M" "V1_F" "V2_A" "V2_B" "V3_T" "V3_G" "V3_H" "V4_D"
[9] "V4_G" "V5_T" "V5_X" "V6_Y" "V6_J"

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Or if need a loop, use Map

unlist(Map(function(x, y) unique(paste(y, x, sep = "_")), 
     unname(n.mat), names(n.mat)))

The apply wouldn't work here as the names for each column will be the row.names attribute (even if change the OP's code to names)

Extracting row and column names with its value from matrix

You could use sig_values to subset Pmatrix

cbind.data.frame(colIDs = colnames(Pmatrix)[sig_values[, 1]],
                 rowIDs = rownames(Pmatrix)[sig_values[, 2]], 
                 values = Pmatrix[sig_values])


#    colIDs   rowIDs values
#1 MU101188 MU101188  1.000
#2 MU101188 MU101310  0.506
#3 MU101310 MU101310  1.000
#4 MU101326 MU101326  1.000
#5  MU10251 MU101326  0.806
#6  MU10251  MU10251  1.000

Extracting rows and columns of a matrix if row names and column names have a partial match

An easier option is to reshape to 'long' by converting to data.frame from table, and then subset the rows based on the values of 'Var1' and 'Var2'

out <- subset(as.data.frame.table(a), Var1 == sub("\\d+", "", Var2),
     select =c(Var2, Freq))
with(out, setNames(Freq, Var2))
    aaa1       aaa2       aaa3       bbb1       bbb2       bbb3       ccc1       ccc2       ccc3 
0.01495641 1.57504185 2.32762287 0.42652979 0.41329383 0.07119408 0.64530516 1.39629918 0.17042160 

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Or with row/column indexing

i1 <- match( sub("\\d+", "", colnames(a)), rownames(a))
a[cbind(i1, seq_along(i1))]
[1] 0.01495641 1.57504185 2.32762287 0.42652979 0.41329383 0.07119408 0.64530516 1.39629918 0.17042160

Extract multiple columns from matrix by column-name

Up front: dplyr::select works on frames, not matrices. Fortunately, subset has an S3 method, subset.matrix:

subset(df, TRUE, c(A:C, E))
#   A B        C  E
# A 0 1 19.92053 56
# B 1 2 19.94818 56
# C 2 3 19.97584 56
# D 3 4 20.00349 56

Alternatively, you can "subtract" columns as well.

subset(df, TRUE, -D)
#   A B        C  E         F  G
# A 0 1 19.92053 56        NA NA
# B 1 2 19.94818 56 0.5295139 NA
# C 2 3 19.97584 56 0.4771412 32
# D 3 4 20.00349 56 0.4412616 32

Extract matrix column with it's name

We can use drop = FALSE without converting to data.frame

m1[,3, drop = FALSE]
#        Col3
#Days      9
#Amount 3200

Extracting col/row names from a matrix based on value condition in R

If we are interested in the row/column names, then convert to table, and coerce it to a data.frame and subset

subset(as.data.frame(as.table(m)), Freq > 5, select = c(Var1, Var2))

data

m <-structure(c(0, 1.6898, 7.55815, 4.18765, 4.4806, 4.41775, 3.9795, 
4.1283, 4.255, 4.4811, 1.6898, 0, 7.67225, 4.113, 4.48225, 4.62525, 
3.9288, 4.02495, 4.19675, 4.4686, 7.55815, 7.67225, 0, 7.3129, 
7.23675, 7.46935, 7.29925, 7.41055, 7.4329, 7.28585, 4.18765, 
4.113, 7.3129, 0, 3.8151, 3.35225, 2.886, 3.29, 3.0194, 3.949, 
4.4806, 4.48225, 7.23675, 3.8151, 0, 4.2949, 3.66205, 4.0022, 
3.70005, 2.34825, 4.41775, 4.62525, 7.46935, 3.35225, 4.2949, 
0, 3.42355, 3.6388, 2.27245, 4.23745, 3.9795, 3.9288, 7.29925, 
2.886, 3.66205, 3.42355, 0, 2.48115, 2.97045, 3.6137, 4.1283, 
4.02495, 7.41055, 3.29, 4.0022, 3.6388, 2.48115, 0, 2.9763, 3.92015, 
4.255, 4.19675, 7.4329, 3.0194, 3.70005, 2.27245, 2.97045, 2.9763, 
0, 3.80345, 4.4811, 4.4686, 7.28585, 3.949, 2.34825, 4.23745, 
3.6137, 3.92015, 3.80345, 0), .Dim = c(10L, 10L), .Dimnames = list(
    c("0", "1", "2", "4", "5", "6", "7", "8", "9", "10"), c("0", 
    "1", "2", "4", "5", "6", "7", "8", "9", "10")))

Returning Column Name from Matrix based on value in R

1

Run sapply over columns and find min and then check if the min meets your condition.

colnames(DF)[sapply(DF, min) <= 2]
#[1] "V3"

2

You can also run apply on columns (MARGIN = 2) to see if any value in each column meets the required condition

colnames(DF)[apply(DF, MARGIN = 2, function(a) any(a<=2))]
#[1] "V3"

3

Use arr.ind = TRUE with which. This will give the indices of the values that meet the condition of which. From that, extract the column information [,2].

unique(colnames(DF)[which(DF<=2, arr.ind = TRUE)[,2]])
#[1] "V3"

DATA

set.seed(42)
DF <- matrix(sample(1:9,9),ncol=3,nrow=3)
DF <- as.data.frame.matrix(DF)
DF
#  V1 V2 V3
#1  9  5  6
#2  8  4  1
#3  3  7  2

extract column names from matrix

In your case, p1 is a vector, so you could use names instead of colnames. This should work:

cnames = names(p1)[inds[1]]

How do I retrieve a matrix column and row name by a matrix index value?

First you need to get the row and column of that index using arrayInd.

k <- arrayInd(4, dim(mdat))

You can then get the right name by getting that element of the row and column names

rownames(mdat)[k[,1]]
colnames(mdat)[k[,2]]

Or both at once using mapply:

mapply(`[[`, dimnames(mdat), k)

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